Showing papers in "Philosophical Transactions of the Royal Society B in 1973"

Na-Ca Exchange and Tension Development in Arterial Smooth Muscle

Abstract: Replacement of external NaCl by LiCl, choline chloride or sucrose increased tension of rabbit aortic strips and pulmonary arteries despite little change in membrane potential. The Ca content of the aortic strips increased concomitantly with the tension development. A two- to threefold increment in 45Ca influx could be measured when external Na was removed. 45Ca efflux decreased in Na-free, Ca-free solutions where little or no tension developed and increased in Na-free, Ca-containing solution concomitantly with the increase in tension. The possible significance of a Ca transport mechanism in the cell membrane which depends on Na and Ca (Na-Ca exchange) for the regulation of vascular tone is discussed.

Factors controlling cytoplasmic Ca 2+ concentration

Abstract: The study of cellular Ca $^{2+}$ exchange in smooth muscle has been severely limited by extensive extra-cellular Ca $^{2+}$ binding. This problem was solved by using La $^{3+}$ to trap Ca $^{2+}$ inside the cells while displacing extracellular bound Ca $^{2+}$ . It was then shown that cytoplasmic Ca $^{2+}$ could be raised by Ca $^{2+}$ influx during high K $^+$ depolarization, Na $^+$ elimination and high pH. Ca $^{2+}$ influx was inhibited by other multivalent cations, local anaesthetics and low pH. In the rabbit aortae norepinephrine and angiotensin increase cytoplasmic Ca $^{2+}$ by release from intra-cellular membrane surfaces. In this same smooth muscle relaxation is brought about by intracellular Ca $^{2+}$ binding. Evidence from vascular, uterine and intestinal smooth muscle demonstrates that the large transmembrane Ca $^{2+}$ gradient depends on cellular [ATP] but not on the Na $^+$ gradient. ATP depletion abolishes the Ca $^{2+}$ gradient by increasing Ca $^{2+}$ influx.

Organization of the outer synaptic layer in the retina of the larval tiger salamander.

Abstract: The organization of the outer synaptic layer in the salamander retina was studied electronmicroscopically in serial sections of tissue prepared by conventional techniques or stained by the method of Golgi. Rod cell pedicles make ribbon junctions on cone cell processes, and rod cell processes invaginate cone pedicles without otherwise making any specialized contact with them. Horizontal cells make ribbon and distal junctions with the photoreceptor cell pedicles; a single horizontal cell may contact both rods and cones. Bipolar cells were observed to make either ribbon or basal junctions with the photoreceptor cell pedicles; in addition, certain processes believed to belong to bipolar cells make both ribbon and basal junctions with the same or different pedicles. A single bipolar cell may make contact with both rods and cones. Horizontal cells synapse on bipolar cell dendrites and on certain unidentified processes which in turn are also presynaptic to bipolar cells. Ascending branches of these processes invaginate deeply the rod and cone pedicles without otherwise engaging them in any junction. Horizontal cell processes are linked by two kinds of junctions: close membrane appositions, and contacts analogous to the distal junctions between horizontal cells and rod pedicles.

The erythroid cells and haemoglobins of the chick embryo.

Abstract: The changes in the types of erythroid cells produced during embryogenesis of the chick have been correlated with the changes in the types of haemoglobins found in the embryo. Primitive erythroid cells constitute the only red blood cells of 2- to 5-day embryos. The first recognizable immature definitive erythroid cells appear in the embryonic circulation at 5 to 6 days and progressively replace the primitive cells, such that by 14 to 16 days the primitive cells constitute less than 1% of the circulating erythroid cells. Primitive erythropoiesis is strikingly different from definitive erythropoiesis. At any one time point between 2 and 16 days, all of the isolated primitive cells appear, by morphological criteria, to be at the same stage of maturation, and, although variation in cell size is observed, for an individual maturation stage, the small cells are not more mature than the medium-size cells, nor are the large cells less mature than the medium or small cells. Maturing primitive erythroid cells undergo the progressive changes in cell structure characteristic of erythroid maturation in mammalian erythropoietic systems, but do so as a uniform cell population. Haemoglobin, isolated from primitive erythroid cells of 2- to 5-day embryos, shows two components on polyacrylamide gel electrophoresis, haemoglobin E and haemoglobin P. The haemoglobin E/P ratio is constant in lysates from 2- to 5-day embryos. At 6 to 7 days when the first haemoglobinized immature definitive erythroid cells appear in the embryonic circulation, two new haemoglobin components are observed in lysates of erythroid cells. These two new haemoglobin components are electrophoretically and immunologically identical to the two haemoglobin components of adult chickens, haemoglobins A and D. As the definitive erythroid cells replace the primitive erythrocytes in the embryonic circulation, the haemoglobins A and D increase in amount and replace haemoglobin P. Haemoglobin P cannot be detected immunologically in erythroid cell lysates from 16-day embryos which contain less than 1% primitive cells. In erythroid cell lysates from late embryos, which contained few, if any, primitive erythrocytes, a minor haemoglobin, electrophoretically similar to haemoglobin E on pH 10.3 polyacrylamide gels, is consistently observed. This component differs from haemoglobin E on pH 8.9 polyacrylmide gels, on Sephadex G-100 columns, on polyacrylamide gels of different porosities, and shows a reaction of only partial identity with haemoglobin E by two-dimensional immunodiffusion. This haemoglobin component, haemoglobin H, is detectable electrophoretically in lysates from 12-day embryos and immunologically in lysates from 8-day embryos. Haemoglobin H has not been observed in adult chickens. The switch from the production of primitive to definitive erythroid cells during development of the chick embryo is associated with the initiation of synthesis of three new haemoglobins, the two adult haemoglobins and haemoglobin H. The haemoglobin D/A ratio of adult chicken haemoglobin, determined from the ratio of gel scan peak masses, is 0.30. When haemoglobins D and A first appear in erythroid cell lysates from 6- to 7-day embryos, the haemoglobin D/A ratio is about 0.9. The D/A ratio of lysates falls to 0.5 by 16 to 18 days, a time when 99% of the erythroid cells of the embryo are mature definitive erythrocytes. However, the haemoglobin D/A ratio of lysates from late embryos and young chicks of 0.5 to 20 days of age is consistently greater than that of adult chicken haemoglobin. Definitive erythrocytes of chick embryos and young chicks appear to differ from definitive cells of adult chickens in at least two ways: the presence of haemoglobin H and the higher haemoglobin D/A ratio.

Observations on the Vegetation of Northeastern Mato Grosso: I. The Woody Vegetation Types of the Xavantina-Cachimbo Expedition Area

Abstract: The Xavantina-Cachimbo Expedition worked during 1967-9 in a 20 km square around a base camp (12 $^\circ$ 49' N, 51 $^\circ$ 46' W), ca. 260 km north of Xavantina (NE Mato Grosso) and near Xavantina itself. The vegetation is of special interest because the base camp is situated near the junction of the savanna region of Central Brazil and the Amazonian forest. It is a pattern of savanna (cerrado), savanna woodland (cerradao), forest and treeless grassland (campo) with often remarkably abrupt boundaries between the different communities. Until 1967 the area had been very little affected by man. The climate is characterized by high temperature throughout the year, an annual rainfall of about 1200 to 1400 mm, and a more or less rainless dry season from June to September inclusive. During the dry season the cerrado, campo and some forms of cerradao vegetation are subject to fire, but are not burned every year. The forest, except the Deciduous Seasonal forest, is not normally burned. The rocks consist of sandstones overlying shale and mudstones. The sandstone weathers to form widespread dystrophic soils of low nutrient content, whilst the finer textured rocks, exposed in some deeper valleys, produce somewhat richer mesotrophic soils. The woody vegetation types of dystrophic soils are classified into three types of Evergreen Seasonal forest ('Swampy Gallery' forest, 'Valley' forest and 'Dry' forest), cerradao and cerrado. The Swampy Gallery forest is found along streams where the water table is close to the surface even in the dry season and is often bordered on one or both sides by strips of campo. In composition it resembles an impoverished Amazonian rain forest. The top-storey is dominated by Qualea ingens and Q. wittrockii, growing sometimes to 40 m, and the undergrowth includes numerous dicotyledons, Scitamineae, grasses and other monocotyledons. At a slightly higher level in stream valleys there is another type of tall forest, Valley forest, in which characteristic trees (all growing to about 40 m) are Apuleia molaris, Copaifera langsdorfii, Hymenaea stilbocarpa and Ormosia sp. (Tento). Much the most extensive type of Evergreen Seasonal forest is the Dry forest which represents the southern fringe of the Amazonian forest and covers a vast area stretching away northwards from the base camp area. This is a mixed community in which the trees seldom grow to more than 20 m. The most abundant species of the upper storey in the area studied are Chaetocarpus echinocarpus, Licania blackii, L. kunthiana, Sacoglottis guianensis and Xylopia amazonica. The transition from Dry forest to cerrado is sometimes abrupt, but elsewhere there is an ecotone in which Hirtella glandulosa cerradao forms a recognizable nodum, occupying a zone up to 4 km wide. Characteristic species in this are Emmotum nitens, Sclerolobium paniculatum and Vochysia haenkeana, as well as H. glandulosa. The boundary between cerrado and Dry forest appears to be dynamic and there are some indications that the forest has recently invaded the cerrado. The present boundary does not seem to be primarily dependent on climate or burning but shows some relation to soil conditions, though apart from a higher clay content in the latter the cerrado and forest soils are much alike. Cerrado has a lower degree of crown cover than cerradao; it is a type of open savanna with grassy undergrowth and is extremely variable in floristic composition and no clearly defined associations could be recognized. The boundary between cerrado and campo in valleys is sharp and appears to be determined by the height of the water table in the wet season. The mesotrophic soils are occupied by Deciduous Seasonal forest, the only woody community in the area in which the top storey becomes leafless in the dry season. The floristic composition of this community is very different from that of the other forest types and characteristic top-storey species include Cedrela fissilis, Piptadenia macrocarpa, Platypodium elegans and Sterculia striata, with Acacia polyphylla and Bauhinia cupulata as a second storey. Bamboos and the palm Acrocomia sp. are features of the under-growth. Floristically this community is similar to forest types found on calcareous rocks in Goias and Minas Gerais. It is fringed by a characteristic cerradao, termed Magonia pubescens/Callisthene fasciculata cerradao.

Cell development in the anther, the ovule, and the young seed of Triticum aestivum L. var. Chinese Spring

Abstract: The developmental behaviour of reproductive cells was studied during premeiotic mitotic activity, premeiotic interphase, meiosis in anthers and ovaries, microsporogenesis, megasporogenesis and embryo and endosperm growth in Triticum aestivum L. var. Chinese Spring. Particular attention was paid first to the timing and rate of cell development in the anthers and the ovary within a floret and secondly , to the timing and rate of nuclear and cell development in the young embryo and endosperm. At 20 °C the development studied lasted in each floret about 21 days starting 7 days prior to meiosis in anthers and ending 5 days after anther dehiscence and pollination. The durations of up to twenty successive cell cycles were estimated. In anthers of plants grown at 20 °C the durations of the three successive cell cycles immediately prior to the cycle which ends at first anaphase of meiosis were about 25, 35 and 55 h respectively. The increase in cell cycle time was correlated with an increase in the size of archesporial cells and their nuclei. A progressive increase in the durations of successive cell cycles as meiosis is approached has not been measured previously in a higher plant species, although it has been noted in the germ line cells of male mice. The pollen mother cells (p.m.cs) within an anther were synchronized prior to meiosis by having their development blocked somewhere in G 1 of premeiotic interphase. The developmental hold began to operate about 103 h prior to the synchronous onset of meiosis in all the p.m.cs within an anther at 20 °C. About 55 h later, when the last archesporial cell completed its final premeiotic mitosis, all the p.m.cs had accumulated in G 1 of premeiotic interphase and synchrony was complete. Premeiotic interphase after all the p.m.cs were first synchronized in G 1 until the synchronous onset of meiosis lasted about 48 h. During this period the G 1 developmental hold was released and p.m.cs initiated DNA synthesis synchronously about 12 to 15 h prior to the start of leptotene. Meiosis in p.m.cs lasted 24 h at 20 °C. Within each floret, meiosis in p.m.cs was almost or quite synchronous with, and had the same duration as, meiosis in the embryo sac mother cell. The Q 10 for meiosis in p.m.cs over the temperature range 15 to 25 °C was about 2.3. Microsporogenesis from tetrad stage until anther dehiscence lasted about 7.5 days at 20 °C. The first pollen grain mitosis (p.g.m. 1) occurred 2.5 days and second pollen grain mitosis (p.g.m. 2) 5.0 days after the end of meiosis. Concurrent with p.g.m. 1 the functional megaspore in the ovule of the same floret divided. This division was rapidly followed by two more synchronous division cycles (also concurrent with p.g.m. 1) which produced an 8-nucleate embryo sac. By p.g.m. 2 the embryo sac contained 20 to 30 antipodal cells at its chalazal end. The antipodal cells subsequently became highly polyploid and some eventually contained up to 200 times as much DNA as haploid egg nuclei. At 20 °C the sperm nuclei reached the egg and polar nuclei about 40 min after pollination. The primary endosperm nucleus divided about 6 h after pollination while the zygote did not divide until about 22 h after pollination. The endosperm often contained 16 mitotic nuclei 24 h after pollination. The nuclear division cycle during the first five division cycles was about 4.5 h. Until the tenth division cycle when the endosperm became a cellular tissue, development of endosperm nuclei was synchronous, but thereafter synchrony was progressively lost. Early embryo development was marked by a gradual decrease in the durations of successive cell cycles. This decrease was apparently correlated with a decrease in the size of embryo cells and their nuclei. Nuclear and cellular developmental rates at 20 °C were very variable. Estimates of nuclear cycle times ranged from about 60 h in the microspore to about 4.5 h in some endosperm nuclei. Nuclear volume was also very variable and ranged from about 240 μm 3 for sperm nuclei in mature microspores to about 160000 μm3 in some polyploid antipodal cells. Both the wide range of nuclear types described, and the speed with which nuclear characters changed, illustrates the remarkable plasticity of the wheat nucleus which may occur in several very different forms. A comprehensive and integrated study of development at the cellular level in reproductive tissues of a higher plant species is presented. The importance of this study is twofold. First, it allows the comparison of reproductive cell behaviour in a higher plant species and in those animal species which have been intensively examined. Secondly the availability of a description of ‘normal’ development under controlled conditions in euploid plants of Chinese Spring opens the way for comparative studies using the wide range of available mutant or chromosomally different genotypes of Chinese Spring which are known to vary in their reproductive development.

The nervous release and the action of substances which affect intestinal muscle through neither adrenoreceptors nor cholinoreceptors

Abstract: Mammalian gastrointestinal muscle is supplied by non-adrenergic, intrinsic inhibitory neurons. The substantial evidence which exists to suggest that adenosine triphosphate is the transmitter released from these nerves is discussed briefly. It is shown that the intrinsic inhibitory neurons compose the efferent link in a cascade of descending reflexes extending from the oesophagus to the anal sphincter. Gastrointestinal muscle is also supplied by non-cholinergic excitatory nerves. The pharmacology of transmission from a group of such nerves to the smooth muscle of the guinea-pig proximal colon is described and evidence is presented to suggest that 5-hydroxytryptamine (5-HT) may be the transmitter substance. The contraction is blocked by phentolamine and methysergide which both antagonize the contractile action of 5-HT. When the muscle is desensitized by continued exposure to 5-HT, the non-cholinergic contraction can no longer be elicited.

Filament Organization in Vertebrate Smooth Muscle

Abstract: Thin (actin), thick (myosin) and intermediate filaments are described in vertebrate smooth muscle. The thick filaments are present in relaxed, contracted, stretched and unstretched vertebrate smooth muscle and bear lateral projections suggestive of cross-bridges. The relatively regular thick filament lattice of the rabbit portal-anterior mesenteric vein can be aggregated by hypertonic solutions and excessive stretch. The intermediate filaments are morphologically distinct and clearly not breakdown products of thick filaments.

Fine Structure of Smooth Muscle

Abstract: The size of smooth muscle cells is different in different organs but varies little within the same tissue. Great changes in cross-sectional area are observed in distended and contracted smooth muscle cells and during contraction and relaxation in neighbouring layers. Two basic types of intercellular junction are described: (a) attachment plaque, where myofilaments end and where the intercellular gap is wide; (b) nexus, where the adjoining cells come close together; the gap or the degree of fusion of membranes is affected by preparation procedures. The occurrence of nexuses is generally correlated with electrical coupling, although sometimes, e.g. in intestinal longitudinal muscle, there is electrical coupling but nexuses are virtually absent. Caveolae are spread over the surface of smooth muscle cells. They appear early in embryonic development. It is suggested that they represent a compartment situated between extracellular space proper and intracellular space; its ionic composition may be more readily controlled by the muscle cell itself. Caveolae disappear from muscle cells after treatment with hyaluronidase in vitro. Sacs, cisternae and tubules of sarcoplasmic reticulum are observed in the superficial region of cells in visceral muscles, closely related to caveolae and plasma membrane. Mitochondria are frequently associated with the reticular system. The suggestion that sarcoplasmic reticulum may play a similar role in smooth muscle as in skeletal muscle, in storage and release of calcium, is discussed. Accumulation of divalent cations by sarcoplasmic reticulum and the effect of incubation in Ca-rich solutions support this interpretation, although the crucial evidence for it is still lacking.

The evolution of an atoll: the depositional and erosional history of Aldabra

Abstract: The earliest sediments identified of late Pleistocene age are quiet-water calcarenites, containing abundant molluscs but few corals. As waters shallowed these were replaced by emergent intertidal sediments, probably colonized by mangroves. Further emersion into subaerial conditions resulted in cementation and solution of the limestones to form a dissected karst topography. Perhaps concurrent with this, phosphates, probably originally derived from sea birds, were deposited in open cavities. Further marine withdrawal caused the erosion and re-deposition of these phosphatic sediments at a lower level. A succeeding event was the formation of a sand cay at the western end of the atoll. Its emergent surface was colonized by tortoises, birds, crocodiles and snails, and the youngest deposits indicate the presence of at least seasonal bodies of standing fresh water. This terrestrial interlude was followed by inundation by a sea, perhaps 2-3 m higher than the present level, in which was deposited a fairly uniform limestone over the whole area of proto-Aldabra. The limestone consists largely of calcareous algae set in a calcilutite-calcarenite matrix, in which both corals and molluscs are low in numbers and diversity. The emergence that followed caused widespread erosion and the island formed, surrounded by low cliffs, was subject to solution fretting and a limited deposition of soils. Renewed submergence carved proto-Aldabra into a broad shallow bank, with an almost flat ring-like rim around the periphery, while re-emergence allowed deposition on this bank of a series of sandbanks, beaches and terrestrial soils. These deposits were truncated by a marine erosion surface which marked the beginning of a sea-level rise that continued to a level at least 8 m above present datum, proto-Aldabra (125000 years b.p.) then consisting of a shallow bank covered by coral-rich calcarenite. Coral growth was more prolific around the rim, but coral knolls were also common within the rim to the northwest, where both coral and mollusc diversities are highest. The dominant sediment in the southeast is a Halimeda -rich sand with relatively little coral growth, but the presence of abundant Acropora around the southeast rim suggests that the dominant wind was from this quarter. Early in the deposition of this rock unit a sea-level oscillation resulted in temporary emergence, causing a change in facies or a break in deposition. A subsequent drop in sea level resulted in the cutting of a terrace at about 8 m and a more conspicuous terrace at around 4 m. Aldabra then stood as a ring of narrow, low, rocky islets surrounding a broad shallow lagoon. Deposits with a land-fauna including crocodiles, tortoises and lizards possibly date from this period. Continued depression of the sea level as a result of the Wurm/Wisconsin glaciation left Aldabra as a steep-sided rocky island, perhaps up to 100 m high. This was well vegetated, and a high rainfall caused much solutional erosion. Sea level, in response to post-Glacial climatic warming, has risen to its present position, a principal consequence being the breaching of the land rim and the flooding of the lagoon to reduce the land area by almost 60 %. Small cavity-fill deposits, caves, and stromatolitic coatings have been formed since the last interglacial, but it is difficult to place them in sequence. A restless history, of changes in the size, shape and character of Aldabra had important effects upon both the marine and terrestrial biotas. The giant tortoise, Testudo gigantea , was eliminated and has recolonized the area on at least two occasions; and the faunas and floras characterizing the sediments of each marine event are very different in composition. The evidence presented does not accord with the popular view of reef growth as steady accretion. The limestones were formed as discrete increments, often with dramatic facies changes between one unit and the next.

Adrenergic influences on uterine smooth muscle

Abstract: 1. The mechanism of β adrenergic inhibition of pregnant rat myometrium was investigated. 2. Isoproterenol (4 x 10 -7 mol/l) caused membrane hyperpolarization of about 12 mV . The magnitude of this hyperpolarization was unaffected by K-free and Cl-free (isethionate substitution) solutions, and was reduced by about 50 % in the presence of ouabain (10 -3 mol/1) and at 10 °C. Hyperpolarization was calcium -dependent, was partially reduced by 12.5 mmol/1 [Ca 2+ ]0 and was abolished when 2.0 mmol/1 La was added to the bathing solution. 3. Isoproterenol (4 x 10 -7 mol/1) increased tissue cyclic AMP levels with a time course paralleling that of the relaxation both at 37 and at 10 °C. Papaverine (10 -4 mol/1) also showed similar actions. 4. Tissue calcium content as measured by the lanthanum technique increased during a K induced contracture and decreased when isoproterenol (4 x 10 -7 mol/1), papaverine (10 -4 mol/1), or dibutyryl cyclic AMP (10 -3 mol/1) relaxed the K contracture. 5. Another relaxant, D-600, a methoxy derivative of verapamil, (10-5 mol/1) had no effect on membrane polarization, tissue cyclic AMP or tissue calcium content. 6. It is concluded that there is an active component to the β adrenergic hyperpolarization of the rat myometium, although an electrogenic sodium pump is not likely to be involved. Rather an electrogenic calcium pump, possibly activated by cyclic AMP, is consistent with the data obtained. Moreover, a mechanism in which cyclic AMP stimulates calcium extrusion may underlie the adrenergically mediated relaxation in the myometrium .

Sarcoplasmic reticulum and mitochondria as cation accumulation sites in smooth muscle.

Abstract: A tubular system of sarcoplasmic reticulum that is not penetrated by extracellular markers is described in vertebrate smooth muscles. The sarcoplasmic reticulum forms fenestrations around the surface vesicles and also forms close appositions (an approximately 10 to 12 nm gap traversed by periodic electron dense materia) with the non-specialized surface membrane. The morphological couplings are considered to be the most probable sites of electromechanical coupling of the action potential to the twitch contraction. The relative volume of the sarcoplasmic reticulum varies in functionally different (tonic and phasic) smooth muscles, and correlates with the ability of the different smooth muscles to contract in the absence of extracellular calcium. Electron opaque deposits of strontium are accumulated by peripheral and central elements of the sarcoplasmic reticulum. The accumulation of strontium and barium by mitochondria raises the possibility that, in addition to the sarcoplasmic reticulum, mitochondria may play a role in the regulation of intracellular divalent cation levels in vertebrate smooth muscle.

The History of the Vegetation and Flora of Widdybank Fell and the Cow Green Reservoir Basin, Upper Teesdale

Abstract: The stratigraphy of all the major peat deposits on Widdybank Fell and in the Cow Green Reservoir Basin, Upper Teesdale, has been investigated and pollen diagrams prepared. This evidence shows that peat has been forming in the area from the end of the late-glacial, zone III, until quite recently, zone VIII, with the exception of a short period between about 10000 and 8800 B.P. The late-glacial vegetation was replaced only slowly by woodlands which at this altitude never developed a closed canopy even during the post-glacial climatic optimum. From 5000 B.P. onwards these woods were gradually replaced by blanket bog on the drift derived soils and later by grassland on the more porous limestone. Pollen grains from many of the rare species which grow in the area today, e.g. Gentiana verna and Dryas octopetala, have been found in the post-glacial deposits at several different levels including those which formed when the woodlands were at their most dense, thus demonstrating their presence in the area throughout the postglacial and confirming the relict nature of the Teesdale flora.

Factors controlling myogenic activity in smooth muscle.

Abstract: contiibution to the regulation of the Ca distribution across the membrane, probably through Na-Ca exchange and by affecting Ca permeability. Although these functions of Na are important for the generation of spontaneous activity, the primary role of Ca is emphasized since spontaneous activity can be produced in Na-free, Ca containing solution. It is postulated that the internal surface of the membrane has negative sites, to which Ca can be bound, and that the K permeability is increased when the amount of bound Ca at this site is increased. The K permeability would then be reduced when Ca is extruded by an active Ca pump, and this may be the mechanism underlying the pacemaker potential. Many smooth muscles exhibit rhythmic spontaneous contractions. These are caused by electrical activity of the muscle fibres. The pattern and the configuration of this spontaneous electrical activity greatly differ in different types of smooth muscles. Accordingly, any generalization is difficult. The origin of the spontaneous activity seems to be myogenic, since various drugs which interfere with the nervous activity or transmission do not abolish the activity. It seems important, first, to clarify the various components in the electrical activity. In this paper it is assumed that there is one basic underlying component which is metabolically driven and which is responsible for the spontaneous activity in every smooth muscle. The results, obtained mainly from the guinea-pig taenia coli, will be presented and they will be interpreted in connexion with the regulation of the intracellular Ca concentration which, in turn, is probably related to the electrical component underlying the spontaneous activity. Components of electrical activity In spontaneously active smooth muscles, two components of electrical activity, slow waves and spikes, are usually classified, although their shape and amplitude are quite different from tissue to tissue. The relative magnitude of the slow wave and spike also varies with the conditions of the preparation and with the methods employed for recording. Figure 1 shows the electrical activity taken from the guinea-pig oviduct and the effects produced by membrane polarization. The activity was composed of a large slow wave and a spike component. Both depolarization and hyperpolarization had only weak effects on the frequency of spontaneous activity, but the amplitude was clearly modified by polarization. On the rising phase of the slow wave, a notch was often observed, and this became distinctly separated during strong hyperpolarization or following strong depolarization, Figure 2 shows mechanical and electrical activity recorded from the circular muscle of the guinea-pig stomach. The frequency of the slow waves in this tissue was also only slightly affected by membrane polarization, as in the oviduct. In the stomnach also, a notch appeared

The Pleistocene geology of the area north and west of Wolverhampton, Staffordshire, England

Abstract: Two hundred and fifty-two square kilometres of land north and west of Wolverhampton have been mapped on a scale of 1:10 560. This area includes a sequence at Four Ashes which has been designated the type section for the Devensian stage of the British Pleistocene. The last glacial advance into the West Midlands occurred during the Upper Devensian, some time after 30 500 years B.P., terminating along the 'Wolverhampton Line' marked by a pronounced thickening of the till sheet and a concentration of large erratics. The till at Four Ashes overlies a thin series of gravels which had at its base a restricted deposit of Ipswichian date and included many lenses of peat or organic silt ranging in age from ca. 70 000 B.P. to later than 30 500 B.P. (Lower and Middle Devensian) representing a period of fluctuating climate ranging from cool temperate to arctic continental in severity. During this period there was a considerable amount of erosion, resulting in the formation of the 'modern' landscape which has only been modified by glacial deposition and post-till periglacial activity. The earliest Pleistocene deposits found in the region are believed to be glacial outwash gravels, probably of late Anglian age which are overlain by Hoxnian Interglacial silts and clays. These early deposits occur beneath the till sheet of the last ice and extend for at least 10 km south of the Wolverhampton Line as eroded relics of a deep channel filling. Glacio-fluvial gravel sequences post-date the retreat of the Late Devensian ice and are concentrated along the principal drainage lines. Late-Glacial organic deposits indicate that the ice had retreated prior to 13 490 years B.P. in the Stafford region. A periglacial environment followed the retreat of the last ice (as evidenced by ice-wedge casts and ice-wedge polygons) and this is thought to have lasted until the climatic amelioration which started around 12 500 years B.P.

The Secretion and Structural Evolution of the Shell of Thecideidine Brachiopods

Abstract: Secretion of the exoskeleton of Thecidellina barretti proceeds in the same way as in other living brachiopods, but the structure of the mantle edge is different. Mucin cells occupy the core of the outer mantle lobe, and periostracal secretion begins within a slot separating lobate cells charged with secretion droplets from long vesicular cells. The former exude an impersistent mucopolysaccharide film and may be regarded as an integral part of the generative zone; the latter secrete most of the periostracum and, thereafter, the carbonate succession as they become part of the outer epithelial layer of the mantle. The periostracum consists of an outer coat initially differentiated into a triple-unit structure and a polysaccharide layer. It is rarely more than 200 nm thick except at the hinge-line where it forms a narrow fold secreted by columnar cells as a cover to the interareas of both valves. Papillose outgrowths of the mantle (caeca), rich in secretion droplets, arise at the mantle edges at regular intervals and persist throughout life. The distal cells are highly microvillous at first, and as they withdraw from the periostracum they secrete numerous proteinous sheaths (the brush) containing mucopolysaccharides, which become encased within the carbonate succession. As the mineral layer thickens, the caeca retreat with the mantle and periodically secrete proteinous partitions within vacated distal parts of the canals (puncta). The carbonate skeleton mainly consists of acicular and granular calcite forming a primary layer with an internal surface ornamented by tubercles, rhombic bodies, and regularly arranged pits accommodating epithelial cells underlying muscle tissue. The teeth and socket ridges, however, are composed of fibres sheathed in anastomosing proteinous sheets and stacked in alternating rows as in fibrous secondary layers found in most other articulate brachiopods. Superficial traces of fibres also occur as patches and on tubercles in both valves. A similar distribution of secondary fibres is found in T. australis; but fibres are limited to spinose outgrowths in the pedicle valve of T. hedleyi, while incipient fibres develop only on the surfaces of mature teeth in Lacazella mediterranea. Study of the shell fabric of nine fossil genera shows that a continuous fibrous secondary layer occurs in all of the earliest thecideidines. During subsequent evolution the layer became neotenously reduced in the three post-Jurassic Subfamilies of the Suborder; and, although the loss was accelerated in the Lacazellinae, the main change to a sporadic secretion of secondary shell took place during late Jurassic or early Cretaceous times in all three groups. A review of the principal morphological features of thecideidines, on balance, corroborates the evidence of the ultrastructure of the shell that the Suborder was caenogenetically derived from spiriferide rather than strophomenide brachiopods.

An ultrastructural study of axonal changes following constriction of postganglionic branches of the superior cervical ganglion in the rat.

Abstract: Postganglionic branches were ligated or cut 1 to 2 mm from the superior cervical ganglion in 48 Wistar rats. The axons were examined at intervals from 6 h to 143 days postoperatively. At 6 h the axons were swollen for about 0.6 mm proximal to the ligature, the distended segments containing chiefly vesiculotubular smooth endoplasmic reticulum , 60 to 110 nm dense-cored vesicles and some mitochondria. These organelles were tightly packed close to the ligature and dispersed in amorphous axoplasm further away. Over the next 12 to 30 h many mitochondria became grouped in compact clusters, associated with filaments, near the proximal end of the zone of densely packed organelles, and other organelles appeared in increasing numbers in the same region. These included clumps of small vesicles (some with dense cores), multivesicular bodies of regular form, loops or flattened sacs of membrane, and tubules with an electron-dense content (all of which were probably transported from the cell bodies), and autophagic vacuoles and large cytoplasmic dense bodies, which appeared to form locally within the intra-axonal accum ulations. The autophagic vacuoles and dense bodies formed part of a reaction of intra-axonal digestion of the material initially accumulated. This digestive reaction coincided with the onset of a phase of intracytoplasmic digestion in the cell bodies. The flattened sacs of membrane and the tubules with electron-dense content, and possibly also the multivesicular bodies, appeared to provide material for the intra-axonal formation of autophagic vacuoles and dense bodies. Close to the ligature the tips of the congested axons degenerated and were phagocytosed by Schwann cells. Regenerative axon sprouting (not described in detail in this paper) began within 24 to 38 h and was associated with the appearance of a wispy material in the axons. It was concluded that the relative output of various types of material from the cell bodies may change during the retrograde reaction to axonal injury in these neurons, as part of a coordinated response involving correlation of events in widely separated parts of the neuron.

Pleistocene Helophorus (Coleoptera, Hydrophilidae) from Borislav and Starunia in the Western Ukraine, with a Reinterpretation of M. Lomnicki's Species, Description of a New Siberian Species, and Comparison with British Weichselian Faunas

Abstract: The five Helophorus species described by Łomnicki (1894) from fossils in oil-impregnated Pleistocene silts at Borislav, near Lvov, are redescribed and indentified as modern species. Four of Lomnicki’s names fall into synonymy, but the fifth, H. praenanus , replaces H. jacutus Poppius for an eastern Siberian species. The fossil Helophorus collected along with the Woolly Rhinoceros by the University of Krakow expedition to Starunia in 1929 are identified, and nine species, all still extant, are present in the sample. These include four species which today live over much of Europe, two which are exclusively eastern Siberian, one found in both eastern Siberia and arctic North America, and two which are widely distributed over Siberia and extend into northern Europe and North America. It is concluded that the climate at Starunia during the period when the deposit was laid down was colder and more continental than at present, but it is stressed that since the assemblage of species found as fossils at Starunia does not exist in any one place today, there may be no exact modern climatic equivalent to Pleistocene Starunia. The Starunia Helophorus fauna is compared with the O rthoptera as described by Zeuner (1934). In both cases there is a mixture of European and Siberian species, but the O rthoptera differ from the Helophorus in including a num ber of montane species. Neither group contains any species today found only in the high arctic. The Starunia deposit has been 14 C dated at about 23000 years B.P., and its fauna is compared with British faunas from the same general period of the last glaciation. The faunas are broadly similar, but the Starunia fauna shows evidence of greater dampness perhaps associated with the period of maximum Weichselian glacierization. The Siberian Helophorus formerly included in H. hrevipalpis Bedel, present in both the Starunia sample and British deposits, is shown to be a distinct species, and is described as H. aspericollis , sp.nov.

Structure and electrical properties of the autonomic neuromuscular junction

Abstract: A description is given of the autonomic neuromuscular junction and of the junction potentials which occur in smooth muscle bundles during transmission. The structural and electrical constants of these muscle bundles have been determined and used to develop an electrical model of the bundle. This has then enabled an analysis of the origin and distribution of current generated by transmitter released from autonomic nerves within the bundle.

The subunit structure of gizzard myosin.

Abstract: Gizzard myosin consists of two m ajor subunits, ‘heavy chains’, with chain masses of about 200000 and two minor com ponents ‘light chains’ with chain masses of 20000 and 17000. Quantitative densitometry indicates that the two types of light chains occur in non-stoichiom etric amounts in a myosin molecule, both in purified myosin preparations and in the whole muscle. Chemical studies on the isolated light chains reveals little chemical similarity between the two types, and preliminary sequence work on the thiol peptides of these light chains further suggests that they may be chemically distinct from those of skeletal and cardiac myosins. Although the exact function of the light chains remains speculative, there is evidence to suggest that the presence of one of the light chains is not required for the hydrolytic activity of this myosin.

The Ordovician Fossil Lagynocystis pyramidalis (Barrande) and the Ancestry of Amphioxus

Abstract: Lagynocystis pyramidalis (Barrande) from the marine Lower Ordovician of Bohemia (Sarka Formation (Llanvirn)), has features which suggest that it is ancestral, or nearly so, to living cephalochordates such as amphioxus (Branchiostoma). L. pyramidalis belongs to a strange group of fossils classified by some workers as 'carpoid' echinoderms (phylum Echinodermata, subphylum Homalozoa, class Stylophora). They are better seen, however, as primitive chordates with echinoderm affinities (phylum Chordata, subphylum Calcichordata Jefferies, 1967, class Stylophora). The most striking echinoderm-like feature of the calcichordates is their calcite skeleton with each plate a single crystal of calcite. Their chordate characters include: (1) branchial slits; (2) a postanal tail (stem) with muscle blocks, notochord, dorsal nerve cord and segmental ganglia; (3) a brain and cranial nervous system like those of a fish; and (4) various asymmetries like those of recent primitive chordates. The calcichordates are divided into a more primitive order, Cornuta, and a more advanced order Mitrata, which evolved from Cornuta. L. pyramidalis is a specialized member of the order Mitrata. Forms up till now associated with it in the suborder Lagynocystida of the Mitrata are better separated from it to form a new suborder Peltocystida (Kirkocystidae plus Peltocystidae). The features which ally L. pyramidalis to amphioxus are as follows: (1) a median ventral atrium opening by a median ventral atriopore; (2) a probably excretory posterior coelom which could give rise to the nephridia of amphioxus by upward growth of the gill slits; (3) evidence that the anus opened externally on the left; (4) evidence that the mouth and buccal cavity was innervated more strongly from the left than from the right; (5) evidence suggesting that, if it swam, L. pyramidalis would rotate about its long axis, clockwise as seen from behind, like late larval amphioxus and larval tunicates. The amphioxus-like features of L. pyramidalis are imposed on the pattern of a very primitive mitrate. There existed thus: (1) a well-developed brain and the cranial nerves were more of the vertebrate pattern than those of amphioxus; (2) left and right branchial openings in addition to the median atriopore; and (3) the tail or stem had paired segmental ganglia. The latest common ancestor of vertebrates and amphioxus would be a primitive mitrate. It follows, since Lagynocystis had a calcite skeleton, that such a skeleton has been lost at least twice in the evolution of the chordates.

A revision of the subfamily Haplorchinae Looss, 1899 (Trematoda: Heterophyidae). II. Genus Galactosomum.

Abstract: A taxonomic revision of the genus Galactosomum is proposed within the context of a revision of the subfamily Haplorchinae. The interpretation of the ventrogenital complex underlying the present revision is re-stated in phylogenetic terms in order to call attention to the differentiation of ventral sucker and gonotyl, and of genital sinus, genital sac, and ventrogenital sac. It is inferred from the multiplicity of structure in the terminal genitalia of digenetic trematodes in general, and heterophyids in particular, that they are cross fertilizing despite being hermaphroditic. It is also suggested that variations in terminal genitalia may constitute an important mechanical element in isolating mechanisms that separate closely related species. A general discussion is presented of the taxonomic significance of characters of the following; ventral sucker, gonotyl, lateral pocket, musculature of ventrogenital sac, seminal vesicle, prostatic ejaculatory duct, excretory bladder, vitellaria, body shape, egg size, shape of testes, pharynx, course of uterus, and gland cells. The materials of the revision comprise known specimens, published accounts of these, and new specimens collected in Australia and borrowed from overseas. Wherever possible, types were examined; thus, of 13 species redescribed, types were studied of 11 species, and other specimens of the remaining two. An attempt was made to verify published records by recourse to the specimens on which the records were based; although only partially successful, verification of a number of records has allowed more accurate assessment of host-specificity and geographic distribution of some species.

Functional morphology with particular reference to hinge and ligament in Spondylus and Plicatula and a discussion of relations within the superfamily Pectinacea (Mollusca: Bivalvia).

Abstract: Excluding the isomyarian family Dimyidae, the Pectinacea comprise the families Propeamussidae, Pectinidae, Spondylidae and Plicatulidae. Present investigations are primarily concerned with species of the last two, both of which are cemented by the right valve, with secondary teeth and sockets which form ball and socket joints between the valves. Neither has previously been examined in life or the hinge and ligament critically studied. Comparing throughout with conditions in the Pectinidae, the ctenidia in Plicatula are simpler (like those of Propeamussium ) but both here and in Spondylus the ciliary pattern (type B (1a)) is more primitive. Spondylus resembles the Pectinidae in that it has elaborate arborescent lips and pallial eyes; Plicatula (and Propeamussium ) has neither, and the inner mantle folds (velum) are reduced (though enlarged in Propeamussium ). The foot is lost in Plicatula and in Spondylus has solely to do with cleansing; the Pectinidae display a range of pedal form and function - from locomotion to byssal attachment and to cleansing. The ratio of ‘quick’ to ‘catch’ muscle in the adductor is associated with habit, being greatest where need for rapid adduction is greatest, primarily in connexion with cleansing, a matter of particular urgency in horizontally disposed bivalves. Pallial eyes - as well developed in permanently attached as in swimming species - are most probably concerned with immediate response to predatory attack on pallial tissues widely exposed when the valves gape. The ligament in both Spondylus and Plicatula is surprisingly different from that in the Pectinidae (and Propeamussidae). The long anterior and posterior outer ligament layers found in the two last which unite the valves at either end of the condensed rounded inner ligament layer are replaced in Spondylus by fused periostracum . The outer ligament layers have migrated inwards and, after dividing on either side of the unchanged inner ligament layer, unite (topographically) above and below it, forming morphologically left and right areas composed equally of anterior and posterior outer ligament layers. The inward extensions of the fused periostracal grooves which form the secondary extensions to the primary ligament may well be associated with the change in nature of the hinge plate (and thus of teeth and sockets) to crossed-lamellar aragonite instead of the foliated calcite present in the Pectinidae. The combined inner and outer ligament layers produce the more powerful ligament demanded by the more massive valves; the secondary periostracal extensions serve only to unite the valves which are maintained in alinement by way of the secondary teeth and sockets. The conspicuous bilateral asymmetry in the hinge and ligament is a result of cementation; similar conditions exist in the cemented pectinid, Hinnites . In Plicatula differences are much greater. Inward growth of the mantle margins results in union above the now submarginal ligament. This is extremely compressed in the transverse plane becoming hoop-like with the right limb the longer. Basally it fractures, although the two halves remain in contact and function is unaffected. As in Spondylus, the halves of the anterior and posterior ligament layers unite on the two sides of the inner ligament layer. Owing to dorsal overgrowth by the hinge plate, the epithelia secreting the outer ligament layers form the two sides and roof of a chamber the base of which is the mantle isthmus (forming the inner ligament layer). Contact with the valves is exclusively by way of the outer ligament layers. The periostracum fuses in the mid-line dorsally and does not contribute to the ligament from which it is separated. Owing to the division of the inner ligament layer into right and left halves, union of the valves is effectively by way of the secondary teeth, here more dorsally extended than in Spondylus but, as there, composed of crossed-lamellar aragonite. Evolution of these four families starts in Palaeozoic stocks with modifications of organs in the mantle cavity - ctenidia, lips, pallial eyes, etc. - proceeding along lines distinct from those involving modifications in the ligament. The former particularly concern the primitive Propeamussidae, largely confined to deep water, and the universally distributed Pectinidae, the latter the Spondylidae and the Plicatulidae. Modifications of the foot have to do with final habit which is invariable freedom in the Propeamussidae, byssal attachment, freedom or cementation in the Pectinidae, and invariable cementation in the Spondylidae and Plicatulidae, the process occurring earlier in the latter and involving loss of the foot. Separation of the Spondylidae from the Pectinidae is more fully established with the present demonstration of the totally different ligamental structure; the difference is so profound in the Plicatulidae as to raise the question of elevating this to superfamily status.

The action of catecholamines on guinea-pig taenia coli

Abstract: Observations of the effects of catecholamines on taenia coli indicate that the α and β actions are exerted on two different enzyme systems both involved in cellular mechanisms which regulate the intracellular Ca 2+ concentration, one by translocation of Ca within the cell and the other by removing Ca out of the cell. The β action reduces the tension response to m em brane excitation, probably by increased Ga uptake at intracellular stores, in all smooth muscles. The α effect is associated with a change in m em brane conductance resulting in hyperpolarization in some, including taenia coli, but depolarization in other smooth muscles. Nevertheless, the underlying mechanism may be the same, i.e. Ca release from intracellular stores and stimulation of Ca extrusion. This hypothesis is based on the assumption that the membrane permeability to K (and hence the membrane polarization and the degree of spontaneous activity) is largely determined by the amount of Ca bound at the inner surface of the plasma membrane. The change in membrane potential and membrane activity produced by the intracellular release of Ca caused by the α-adrenergic action will, therefore, depend on the ratio between the amount of Ca bound at the inside of the cell membrane and the rate of Ca pump activity in individual tissues.

Retinal Structure in Latimeria chalumnae

Abstract: The retina of Latimeria chalumnae contains four types of visual cells; most are rods, and there are three types of cones. Rod outer segments are cylindrical and appearances at their bases suggest that they may be renewed discontinuously from the inner segment. The rods have simple synaptic spherules, each bearing a single basal filament ending in a club-shaped expansion. Type 1 cones contain an oil droplet, and have a complex synaptic pedicle bearing about 12 basal filaments. Type 2 cones have no droplet, and a pedicle bearing about six basal filaments and of complexity between that of rods and type 1 cones. Type 3 cones resemble type 2, except that they have a clear vacuole, but not an oil droplet, in the inner segment. The pigment epithelium contains abundant phagosomes, but pigment granules are absent where the epithelium overlies the choroidal tapetum lucidum. Regular arrays of tubules occur in the cytoplasm, some of which appear to be formed from three interlacing hexagonal nets. Two types of bipolar cell are present. Most are displaced bipolars, with nuclei in the outer nuclear layer. The rest are large, with nuclei in the horizontal cell layer. Both types bear Landolt’s clubs, which penetrate the outer limiting membrane. Their endings contain a cilium complex, and a single large mitochondrion. Some contain 60 nm vesicles, which are also found near disrupted club endings. Two types of horizontal cell are present. A few dark-staining cells with extensive web-like processes occur next to the outer plexiform layer. The expansions of rod basal filaments make contact with these cells. More voluminous pale staining cells with long cylindrical processes occur vitread to the dark cells. Presumed amacrine cells form a layer vitread to the horizontal cells; they and the inner plexiform layer were not well fixed. Sparse ganglion cells occur at the same level as the nerve fibre bundles. Radial fibres penetrate the horizontal cell layer as compact columns. They do not contribute to the outer plexiform or horizontal cell layers, but elsewhere spread amongst the other retinal elements. Their expansions determine the inner contour of the retina. Cells, probably microglial, which contain lysosomes are scattered amongst the other elements. 143000 myelinated fibres are present in the optic nerve, which also contains non-myelinated fibres. Retinal cell counts are given.

Active ion transport and resting potential in smooth muscle cells

Abstract: The diffusion potential in taenia coli cells calculated from the intra- and extracellular ion concentrations and from the calculated membrane permeabilities is less negative than the measured membrane potential. This discrepancy could be due to a continuous contribution of an electrogenic ion pump to the membrane potential. This hypothesis is supported by the finding that the sum of the active ion fluxes is sufficiently large to generate a potential of -20 mV across the membrane. Moreover, an unequivocal electrogenic component of the membrane potential has been demonstrated during maximal activation of the ion pump in K-depleted cells. The importance of this electrogenic component depends on the membrane resistance, a parameter which is very much affected by the experimental procedure. The active Na-K exchange is stimulated by [Na] $\_i$ and [K] $\_o$ and is inhibited by [Na] $_o$ . Furthermore, it has been observed that 47% of the Na-exchange of Na-enriched tissues is due to Na exchange diffusion.

Ion Distribution and Ion Movements in Smooth Muscle

Abstract: The steady-state fluxes of K $^+$ , Cl $^-$ and Na $^+$ from smooth muscles in normal Krebs solution are described, and some of the problems encountered in the interpretation of such results are discussed. Sodium fluxes are particularly difficult to analyse, and the type of model used to estimate sodium permeability from flux curves, determines the value calculated to a large extent. In order to simplify the ionic distribution in the tissue, in the hope of obtaining more information about the handling of Na and K by the guinea-pig taenia coli, potassium-free (high Na) tissues and sodium-free (high K) tissues were prepared by soaking for 4 h in the relevant solution. The tissues reach a steady state, and the effluxes of $^{42}$ K from high K tissues and $^{24}$ Na from high Na tissues were measured and compared. In these two conditions the electrochemical gradients for Na $^+$ and for K $^+$ are probably identical. Nevertheless, the fluxes are markedly different. At 37 $^\circ$ C the Na flux is much faster than the K flux, and a part of the Na exchange is very temperature sensitive. There is also some evidence for a sodium calcium exchange mechanism. It is hoped that further experiments will produce results that will help to understand the processes involved in these exchanges.

The stimulant action of acetylcholine and catecholamines on the uterus.

Abstract: The α action of catecholamines on oestrogen dominated guinea-pig uterus is stimulant. The cell membrane is depolarized, membrane conductance is increased, spike discharge is accelerated and tension develops. This action resembles that of acetylcholine though catecholamines are less potent, and, in equiactive concentrations, catecholamines have a longer latency and a longer duration of action. Evidence, obtained by modifications of the ionic environment, indicates that the depolarization by acetylcholine is due to an increase in sodium and calcium permeability and that acetylcholine can release calcium from intracellular stores. The depolarization by catecholamines is due to an increase in chloride permeability and, in addition, sodium is required for the ensuing increase of spike discharge. Catecholamines produce an increase in the force of contraction, long outlasting their immediate stimulation. Moreover, their effect on membrane potential and membrane conductance persists in the presence of lanthanum. These results suggest that Ca release from intracellular stores may be the primary effect produced by the α action of catecholamines and that the increase in the cytoplasmic Ca 2+ concentration may cause the changes at the cell membrane.

Extractability and properties of the contractile proteins of vertebrate smooth muscle

Abstract: The vertebrate smooth muscles differ from the striated ones by their larger extracellular space, the smaller size of their cells and their high content in extracellular components. Furthermore, the smooth muscle cell is a bifunctional biological unit able to carry on also an important biosynthetic activity. The contractile proteins of vertebrate smooth muscle are extractable at low ionic strength contrarily to those of striated muscle. The partition of the salt extractable nitrogen between the low and high ionic strength extracts is very different in these two cases. Acidification of low ionic strength extracts of vertebrate smooth muscle at pH 5 allows precipitation of the contractile proteins quantitatively together with a large amount of contaminants typical of the smooth muscles. Comparison of the contractile proteins of vertebrate smooth muscle with their striated counterparts shows that actin is a very constant component of the contractile machinery, that tropomyosin holds an intermediate position, while myosin is the most variable. The smooth muscle myosin differs not only by some general properties as salting-out range and thermostability, but also by the behaviour of various parts of the molecule. The globular head has a different ATPase activity and is responsible for the very peculiar immunological behaviour of this myosin. The point along the myosin rod which is attacked by trypsin is much more resistant to proteolysis. The light meromyosin is more soluble and differs very much in amino acid composition. The comparative study of myosin reveals only minor variations from one species to the other but more or less wide ones within each species according to the type of muscle examined.

The Late Pliocene marine formation at St Erth, Cornwall

Abstract: New excavations were made in the long-abandoned sand and clay pits at St Erth, Cornwall, from which rich collections of marine mollusca and foraminifera have come in the past The sediments and stratigraphy revealed are described, and the results of detailed studies of the fossils (mollusca, foraminifera, ostracoda, and plants) in the marine clay are given The sand member is well sorted, and in places contains two fine-sand populations, one of beach and the other of dune origin The clay member was probably deposited not far below low-water mark in a sea whose water temperature was higher than that of Cornwall today, at the time that the final Boytonian beds of the Pliocene Coralline Crag were being deposited in East Anglia, and the Pliocene marnes a Nassa were being deposited at Bosq d'Aubigny in Normandy Sea level appears to have been lowered by about 45 m to its present level since the marine clay was deposited The possibility of crustal movement in Cornwall is referred to