Showing papers in "Proceedings of The Royal Society B: Biological Sciences in 1957"

Virus interference. I The interferon

Abstract: During a study of the interference produced by heat-inactivated influenza virus with the growth of live virus in fragments of chick chorio-allantoic membrane it was found that following incubation of heated virus with membrane a new factor was released. This factor, recognized by its ability to induce interference in fresh pieces of chorio-allantoic membrane, was called interferon. Following a lag phase interferon was first detected in the membranes after 3 h incubation and thereafter it was released into the surrounding fluid.

Interaction at end-plate receptors between different choline derivatives.

Abstract: Interaction between different choline derivatives has been studied by applying them simultaneously to a motor end-plate and recording the resulting changes in the membrane potential of the muscle fibre. Choline potentiates the depolarizing effect of acetylcholine (Ach) when applied in normal Ringer. Decamethonium has a 'diphasic' action, initial depression of the Ach effect being followed by more prolonged potentiation. When these experiments are made after treating the muscle with an esterase inhibitor (prostigmine $10^{-6}$ $\text{w/v})$, the potentiation of the Ach effect, by decamethonium or choline, is absent and replaced by simple 'curare-like' inhibition. When decamethonium is allowed to interact with a rapidly acting stable ester (carbaminoly-choline or succinylcholine), it produces simple 'curare-like' inhibition. The triple effects of choline and decamethonium, i.e. (i) weak depolarization, (ii) potentiation of Ach in normal Ringer solution, (iii) inhibition of Ach in the presence of prostigmine, can be explained by competitive reactions between the drugs and receptor as well as Ach-esterase molecules. It is suggested that the first step in a depolarizing end-plate reaction is the formation of an intermediate, inactive, compound between drug and receptor.

Virus interference. II. Some properties of interferon.

Abstract: Interferon could be titrated by the amount of interference induced in fragments of chorioallantoic membranes challenged with influenza A virus. Over a ten-fold range, inverse proportion between interferon concentration and haemagglutinin titre reached by the challenge virus was observed. Interferon proved stable at 2 degrees C for 2 weeks. Marked inactivation took place after 1 h at 60 degrees C. Interferon was not measurably sedimented by 100 000 g for $\frac{1}{2}$ $\text{h}$. It was held back by gradocol filters of a.p.d. $0.6\mu $. It was not dialyzable. Interferon was active against influenza A, Sendai, Newcastle disease and vaccinia viruses. It was not neutralized by anti-MEL rabbit serum and only slightly inhibited by pooled human serum rich in complement-fixing antibody to influenza A soluble antigen.

The denaturation of lipid-protein complexes as a cause of damage by freezing.

Abstract: The practice of cold storage for preserving labile material of biological origin is widespread. The general utility of this method and the successful preservation of living cells and tissues in the frozen state has overshadowed the fact that freezing can be a harmful process to living cells (Wood 1956). It used to be thought that the crushing or spearing action of ice crystal growth was the principal source of damage by freezing; indeed so reasonable is this theory that it is difficult to believe that some at least of the harmful effects of freezing are not due to this cause. The development of the theories of damage by ice crystal growth have been described in detail by Luyet & Gehenio (1940), and by Meryman (1956). By contrast with damage on a macroscopic scale which might occur during the growth of ice crystals there is evidence to show that freezing can damage the molecular constituents of living cells, and this is most unlikely to be a direct consequence of the intrusion of ice crystals. This aspect of the problem of freezing damage forms the basis of this paper.

The collagen and elastin content of the arterial wall in the dog.

Abstract: A survey has been made in adult dogs of the collagen and elastin content of the walls of arteries varying in size from the thoracic aorta to the saphenous artery. In all arteries, except the smallest, collagen and elastin together formed about 50% of the dry weight. In the smallest the proportion was somewhat higher. On the basis of relative proportions of elastin and collagen the systemic arterial tree was found to be divided rather sharply into two regions: in the intrathoracic aorta there was about twice as much elastin as collagen in the wall; in all other vessels the relation was reversed, there being about twice as much collagen as elastin. The transition between the more elastic intrathoracic aorta and the more collagenous extrathoracic vessels was abrupt and took place over a distance of only 5 cm or so. The pulmonary artery resembled the extrathoracic vessels rather than the thoracic aorta in ratio of elastin to collagen. Newborn and young puppies showed a similar difference to adults between thoracic and abdominal aorta, although we did not investigate the relation between the two vessels in detail.

The Use of Osmium in the Fixation and Staining of Tissues

Abstract: The use of gallic acid derivatives in the visualization of osmium in tissue sections has been re-investigated. By the use of alkyl esters of gallic acid greatly improved results can be obtained. Fixation with buffered osmium textroxide followed by ethyl gallate affords a simple and reliable method for staining fat droplets, mitochondria, etc. According to the hypothesis put forward the distribution of osmium is determined chiefly by the distribution of unsaturated fatty acids; none is bound by nucleic acids and relatively little by protein. The result is claimed to be an histology based primarily on lipids, which is contrasted with the customary histology based on nucleic acids and proteins. Evidence is given that osmium tetroxide causes polymerization of unsaturated lipids by the cross-linking of ethylenic double bonds. This is particularly liable to occur in layers of oriented lipids. Such layers are widely distributed in living cells; their stabilization by linkage through osmium is considered to play the most important part in cytological fixation by osmium tetroxide.

A study of curare action with an electrical micro-method

Abstract: A micromethod is described by which depolarizing and inhibiting drugs can be applied, ionophoretically, from a common 'point source' to sensitive regions of a motor end-plate The effects of the drugs on the membrane potential of a single end-plate are recorded, in the frog's sartorius muscle The antagonism between d-tubocurarine (DTC) and acetylcholine (or carbachol) is studied with this method Close-range application of small quantities of the depolarizing agents (of the order of several times $10^{-11}$ coulombs, or $10^{-16}$ $\text{M})$ sets up transient potential changes of several millivolts amplitude Application of a somewhat larger quantity of DTC (about $4\times 10^{-10}$ $\text{C)}$ produces a transient 50% inhibition of the acetylcholine (or carbachol) potential Curare does not alter the resting potential, nor the resistance or capacity of the end-plate or muscle fibre, but specifically interferes with the chemo-receptor properties of the end-plate The inhibitory effect of DTC is obtained only with external application, but not with intracellular application from the inside of the muscle fibre The decay of the inhibitory action of DTC is slow compared with the subsidence of the depolarization produced by acetylcholine or carbachol The reason for this difference in time course is examined; it is probably due to relatively slow dissociation of the curare-receptor complex Procaine in close-range, short-time application is as potent an inhibitor of acetylcholine action as DTC The procaine effect subsides, however, much more rapidly than the action of curare

The fine structure of developing bone in the embryonic fowl

Abstract: The fine structure of the tarso-metatarsus of avian embryos has been investigated by means of thin sections in the electron microscope. The morphological features of osteoblasts are similar to those of fibroblasts, and where the organic matrix is just being deposited, fibrogenesis is found to occur in intimate association with the surface of the osteogenic cells. The newly formed collagen fibrils show an axial periodicity of about 640A with a considerable degree of fine structure; densitometer traces demonstrate that five bands and five interbands within a period are normally apparent. As transverse sections of fibrils show that they increase in diameter during development and that each fibril is invested by a less dense interfibrillar material, it must be assumed that this substance contains collagen molecules or their precursors. In the early stages of mineralization of the bone matrix small particles of less than 100A across are localized within the main indentation of each period of the collagen fibrils, namely, between the d and ab bands. Electron diffraction of these sections demonstrates that apatite is present; this indicates that the particles are crystalline in nature. As the particles have been found in sectioned collagen fibrils they must penetrate into the fibrils to some extent; their precise site in the main interband may have a bearing on the mechanism by means of which the apetite crystals ultimately become preferentially orienated with their long axis parrallel to the collagen fibre axis.

Diurnal Changes of Stratification and Photosynthesis in some Tropical African Waters

Abstract: A description is given of diurnal changes, due to the photosynthesis of phytoplankton, in three shallow African waters. Their vertical distribution was largely controlled by changes of thermal stratification; examples corresponding to different degrees of the latter are illustrated from four series of observations. Thermal stratification was generally intermittent, with marked stratification during the day, ended by isothermal mixing at night. An effect of these changes upon the distribution of a blue-green alga, Anabaena, and its photosynthetic activity, is also illustrated. Experimental determinations of the rates of photosynthesis (as milligrams of oxygen produced per unit volume of water, or of algal cells, per hour), and their distribution with time and depth, were obtained using the classic method of suspended light and dark bottles. Photosynthetic behaviour generally resembled that found in temperate waters, but maximum rates of photosynthesis calculated per unit volume of algal cells were unusually high. The preceding observations are used to calculate rates of photosynthesis below unit area of water surface, both from the experimental results and from the diurnal variation of oxygen content in the open water. In the latter case the observed increase of oxygen content in a water column during daytime is corrected for sources of loss, due to respiration and exchange with the atmosphere, using a mean rate of oxygen depletion measured during the night. Although the method is subject to many sources of error, which are discussed, the conclusion is reached that it can provide useful, if often rough, estimates of the rate of primary production. The experimental estimates were calculated both for the experimental periods, and for longer daily periods, using some general equations previously proposed. The calculations from diurnal changes and from experimental data are in agreement concerning the order of magnitude of production, but close conformity was obtained for only one series of observations. The areal values of production estimated from diurnal changes lay in a limited range of 4 to 11 g oxygen (equivalent to approximately 1.5 to 4 g carbon) $\text{m}^{-2}$ $\text{day}^{-1}$, despite considerable variation in individual factors such as population density and underwater light penetration. These values are similar to other estimates for phytoplankton in very productive waters.

The Ferrier Lecture - Inquiries into the anatomical basis of olfactory discrimination

Abstract: Sir David Ferrier, in whose memory I have the honour of giving this lecture, was particularly distinguished for his pioneer experimental studies on cerebral localization. This aspect of his work was stressed by Sherrington, who, in an obituary notice in 1928, wrote that ‘Ferrier placed the question of cerebral localization of function on an absolutely certain basis of experimental fact’. Much of Ferrier’s work in this field was summarized by him in the Croonian Lectures delivered before the Royal College of Physicians in 1890. In the fifth of these lectures he dealt with the evidence for the localization of the ‘olfactory centre’, and it is interesting to note that, while he adduced good evidence for the olfactory functions of those limited areas of the brain which, by modem technical methods, have indeed been established to be receptive areas for olfactory impulses, he expressed considerable doubt on the validity of the evidence adduced by comparative neurologists for including in the so-called ‘rhinencephalon' (i. e. ‘olfactory brain’) such widely distributed parts of the brain as the hippocampus and the cingulate convolution. He pointed out, for example, that the size of the hippocampus in different species of mammal bears no relation to the degree of elaboration of the sense of smell, and he quoted Sir William Turner’s opinion that, in spite of the trivial development of the olfactory apparatus in man, ‘the human hippocampus is absolutely larger than in mammals generally’. However, because of their relationships and apparent connexions (so far as the latter were inferred from the somewhat crude techniques then available), the hippocampus and cingulate convolution, together with quite a number of other related structures, came to be included by comparative anatomists in the comprehensive term ‘rhinencephalon’, and for many years these were accepted as essential components of the cerebral mechanism of olfaction. It is only in recent years that this error has come to be recognized, and it is interesting to consider why the detailed study and elucidation of olfactory pathways by experimental studies have lagged so far behind those of other sensory mechanisms in the brain. One reason, no doubt, is the relative inaccessibility to experimental investigation of the olfactory pathways, for, being situated in the basal region of the cerebral hemisphere, they are not very easily approached by ordinary surgical procedures. Another reason is the difficulty (which Ferrier himself found) of determining in experimental animals the effects of local lesions on the ability to discriminate olfactory stimuli. But during the last fifteen years or so, attention has become increasingly focused on the nervous mechanism of olfaction, and as a result we now have a good deal more information about it. Undoubtedly this has been due in large part to Adrian’s application of electrophysiological methods to the study of the sense of smell, and, in particular, his analysis of the electrical activity of the olfactory bulb evoked by various kinds of odour. But the renewal of anatomical studies of the olfactory pathways has also been partly stimulated by the growing realization that the evidence for the essentially olfactory nature of the greater part of the ‘rhinencephalon’ was in fact very unsatisfactory indeed. Indeed, it was this which made my colleagues and myself recognize the importance of clarifying the precise details of the olfactory pathways, if only because of a suspicion that the assumed olfactory function of the hippocampus and related structures may have long been responsible for their neglect in the study of cerebral functions in general. The results of our experimental investigations of the olfactory pathways made it clear that, in fact, there is no anatomical evidence that the hippocampus and related structures are primarily concerned with olfactory functions, at any rate in the mammalian brain, and this has been confirmed by a number of subsequent studies. But, as so commonly happens in an investigation undertaken with one particular objective in view, our studies led to other observations which seem to be of considerable interest in themselves, particularly because of their relevance to the problem of olfactory discrimination.

The effect of excess vitamin A on cultures of embryonic chicken skin explanted at different stages of differentiation.

Abstract: In earlier experiments, Fell & Mellanby (1953) showed that the simple, two-layered epidermis of the 7-day embryonic chick underwent mucous metaplasia when grown in medium containing excess vitamin A. The present investigation was undertaken to see whether epidermis at more advanced stages of development would undergo a similar transformation in vitro under the influence of vitamin A. Skin from the shank and foot of 13-, 14- and 18-day chick embryos was grown on rayon acetate cloth by Shaffer’s modification of the watch-glass method, in medium (cock plasma and embryo extract) to which natural or synthetic vitamin A alcohol had been added. For purposes of comparison, one experiment was made with skin from the trunk and limbs of 7-day embryos. A dose of 1500 i. u. vitamin A /100 ml. of culture medium completely inhibited keratinization in all the + A explants, whatever the age of the embryo from which they were obtained. This concentration induced mucous metaplasia in all the explants from 7- and 13-day chicks, and in a minority of those from 18-day embryos. In the 13- and 18-day explants, the outer strata of epidermal cells degenerated and were sloughed, and the secretory epithelium was formed from the deepest and least differentiated layers. The dermis also was affected by the vitamin. When the explants were transferred from + A to normal medium, mucin secretion at first increased, often becoming astonishingly copious; later the mucous tissue was shed and the deeper cells regenerated a squamous, keratinizing epidermis. In all the controls grown on normal medium, the epidermis retained its squamous structure and formed increasing amounts of keratin, except at the margin of the 7- and 13-day cultures; here the newly formed epithelium, which had spread beyond or below the dermis, often failed to cornify and in one 7-day control, which elsewhere was heavily keratinized, it even developed some secretory cells. This peripheral effect is thought to be due to the close and prolonged contact of the outwandering epithelium with the fairly high level of vitamin A normally present in fowl blood plasma. The concentrations of vitamin A used in the present experiments were much less than those that can be produced in the blood of fowls fed on a high vitamin A diet. The vitamin A in the culture medium, however, may be much more readily available to the epidermis than the same concentrations of vitamin in the blood stream of a hypervitaminotic bird. It is also probable that the vitamin is in a more active state in the culture medium than it is in vivo (cf. Fell & Mellanby 1952).

The spindle and extrafusal innervation of a frog muscle.

Abstract: In the frog muscle, ext. long. dig. IV, there are two or three spindle systems. Each consists of a bundle of intrafusal muscle fibres with two, three or four discrete encapsulated sensory regions distributed in mechanical series along it. A sensory region is usually comprised of the coiled branches of one afferent axon. These embrace the intrafusal fibres and ultimately form long fine varicose endings on or near them. The intrafusal striations appear to be lost for a short distance within the sensory region, and in this region the intrafusal fibre nuclei crowd together. The ‘small’ extrafusal efferents break up into trusses of fine unmyelinated axons and terminate as ‘grape’ end-plates, several of which can occur on the same muscle fibre. This is the ‘tonic’ system. The ‘large’ extrafusal efferents terminate as ‘Endbiischel’ end-plates on muscle fibres not supplied by grape endings. This is the ‘twitch’ system. Both ‘grape9 and ‘twitch’ end-plates occur on the intrafusal bundle (probably on separate fibres) between the sensory regions. They are supplied by branches of ‘small’ or ‘large’ axons respectively, which also innervate extrafusal fibres. Thus like the extrafusals the intrafusal bundle is composed of ‘tonic’ and ‘twitch’ muscle fibres. This situation contrasts with that of the mammal, where extrafusals are exclusively ‘twitch’ fibres and intrafusals ‘tonic’.

Radiocarbon dating and post-glacial vegetational history: Scaleby Moss.

Abstract: A proportional gas-counter of about 21. volume, within a castle of 5 tons of zinc, enclosing in turn an anticoincidence shield, has been used to make radiocarbon assays of highly purified carbon dioxide at a pressure of 2 atm. A net contemporary count-rate of 27 counts per minute has been secured with a constant background rate of 25. The chief features of this apparatus and of the combustion technique are briefly indicated. The radiocarbon assays have been employed to provide age determinations from a series of peat samples secured from a dry peat-bog at Scaleby Moss, Cumberland. The whole peat sequence has been pollen-analyzed and each radiocarbon sample is very exactly referred to a major zone boundary in a zone sequence which extends from the Late-glacial period continuously through almost the whole of the Post-glacial period. The dates obtained have been based upon an estimated half-life for radiocarbon of 5568 ± 30 years. The errors of determination are of the order (1 S. D.) of ± 150 years. The results are satisfactorily self-consistent, contiguous samples have closely similar dates, and the whole series of dates follows the stratigraphical sequence. It is shown that at Scaleby Moss the Late-glacial/Post-glacial boundary was about 8300 B. C.; The Boreal/Atlantic boundary at about 5000 B. C., and the Sub-boreal/Sub-atlantic boundary at about 3000 B. C. The other zone datings conform with this sequence. This evidence goes some way to establish the synchroneity of the major zones on both sides of the North Sea and indicates the suitability of the method for resolving this type of Quaternary historical problem.

Stress relaxation in muscle.

Abstract: Tension decay following stretch (stress relaxation) has been studied in resting long-fibred smooth and striated muscles. In both types of muscle, tension decays rapidly at first and then more slowly; the decay curve can be resolved into two exponential components, neither of which is significantly affected by changes in temperature or speed of stretch. It is shown that the half-times of fast and slow components of tension decay are related to the intrinsic speed of muscle. A model is proposed which imitates the properties of preshortened resting muscle at lengths where it shows negligible resting tension.

The mechanism of water absorption by roots. II. The role of hydrostatic pressure gradients across the cortex.

Abstract: Using methods described in Part I differences of pressure were applied between the external medium and the xylem elements of tomato root systems. The pressure permeability coefficient $\text{k}\_{p}$ (the water flux per unit pressure difference), and the osmotic permeability coefficient $\text{k}\_{0}$ (the water flux per unit difference of osmotic potential between the external medium and the xylem elements) were compared under similar conditions of applied pressure. Also $\text{k}\_{0}$ was measured in the presence and absence of pressure gradients. The most striking effect of applying a pressure gradient was an increase in $\text{k}\_{0}$, 2 atm commonly causing a five-fold increase. Thus diffusion of water across the cortex was greatly facilitated by a pressure gradient. In addition it was found that under similar pressure conditions $\text{k}\_{p}$ was consistently greater than $\text{k}\_{0}$, $\text{k}\_{p}$/$\text{k}\_{0}$ being about 1.3 with an applied pressure difference of 2 atm. This indicated a mass flow of about a quarter of the total flux under these conditions. This dual nature of the water movement was confirmed by the action of cyanide and anaerobic conditions which caused a greater reduction in $\text{k}\_{0}$ than $\text{k}\_{p}$ showing that the diffusional pathway was more sensitive to decreased metabolism than the mass flow pathway. The effect of pressure gradients on diffusional water movement and the possible location of the mass flow pathway are briefly discussed as are their implications with reference to transpirational tensions and the uptake of solutes from the soil.

The descriptive use of discriminant functions in physical anthropology.

Abstract: The evolutionary status of the fossil Australopithecinae and of the fossil apes belonging to the genus Proconsul has stimulated considerable discussion. Particular attention has been paid to the teeth of the fossils, and many statements appear in the literature comparing their overall dimensions with those of human beings and of the extant great apes. By way of placing such statements on a sound basis, measurements designed to describe the main features of the teeth have been taken on series of skulls of three types of modern man (British, West African native, Australian aboriginal) and of the three living great apes (gorilla, orang-outang and chimpanzee). The statistical treatment of multivariate data of this type is considered. If p measurements are taken on a tooth, the results may be considered as points in a p-dimensional space. If we replace the original measurements by k

Physical limitations of the rapid freezing method.

Abstract: Throughout the recorded history of biological freezing, it has generally been recognized that one may differentiate between rapid and slow freezing, although it has not always been realized how compelling is the distinction which can be drawn between the two on the basis of the markedly different distribution of ice crystals and the differing mechanism of cell injury which may result. In order, therefore, to discuss the physical limitations of rapid freezing, the term must be defined and differentiated from slow freezing. This paper thus becomes primarily a discussion of slow and rapid freezing from which the limitations of the rapid freezing method should become self evident. Possibly the single most important concept in biological freezing as well as the most difficult for the biologist to assimilate is the following: despite the collective and individual complexity of living cells, freezing in a biological matrix represents nothing more than the removal of all available water and its isolation into inert foreign bodies, the ice crystals. Freezing is a wholly physical phenomenon obeying known and simple laws and, tempting though it may be to imbue biological freezing with the same mysterious complexity that surrounds the cells themselves, it is quite unnecessary. The transfer of water out of solution into ice crystals is a very straightforward phenomenon and is, in effect, simply dehydration with the removed water sequestered locally in the tissue rather than entirely removed. From this dual event—dehydration with foreign body formation—stem all the physiological and biochemical events subsequent to freezing (Meryman 1956).

Carotenoids in Daphnia.

Abstract: Carotenoid pigments are found in the gut wall, fat cells and ovary of Daphnia. A carotenoid-protein is sometimes present in the blood; the amount varies during an instar. The carotenoid-protein in the eggs of Daphnia and certain other Cladocera undergoes a change when the embryos are fully developed. The protein link is broken and the freed carotenoid leaves the cytoplasm of the fat cells and intensifies the colour of the fat globules. Light promotes the deposition of carotenoids in the fat cells and eggs of Daphnia magna. Females reared in the light contain three times as much carotenoid as similarly fed females reared in the dark. The carotenoid pigments of D. magna have been identified as $\beta $-carotene, $\gamma $-carotene, lutein (esterified), and astaxanthin (part esterified). This is the first record of $\gamma $-carotene in a crustacean.

Low-temperature storage of mammalian spermatozoa.

Abstract: Experiments in this and other countries on the preservation of spermatozoa at very low temperatures have shown that no mammalian spermatozoa so far examined survive freezing when they are cooled ultra-rapidly from temperatures above freezing point to temperatures of -79 degrees C or below. Slow cooling and the addition of glycerol to the media in which the spermatozoa are suspended, however, permits survival of the spermatozoa of many species. In different animals, there are marked variations in the resistance of their spermatozoa to freezing and the proportion of spermatozoa which can be revived from very low temperatures may be influenced both by the concentration of glycerol added to the semen and by the composition of the diluting fluid. In experiments with the spermatozoa of the bull, ram, stallion and boar it has been found that during slow cooling to -79 degrees C there is a critical temperature range between -15 and -25 degrees C at which the greatest amount of damage occurs. The rate at which the capacity for motility of the spermatozoa is destroyed within this critical temperature range is considerably reduced by allowing the spermatozoa to stand at 2 degrees C in contact with a medium containing egg yolk and glycerol for 18 h before freezing. The extent of damage in the critical temperature range may also be reduced by cooling the specimens at a rate of 0.25 to 0.5 degrees per second between -15 and -25 degrees C.

The mechanism of water absorption by roots I. Preliminary studies on the effects of hydrostatic pressure gradients

Abstract: During transpiration the hydrostatic tension which develops in the xylem conducting elements of the root draws water from the soil through the intervening tissues of the cortex, etc It is uncertain whether this movement is entirely diffusional or in part a mass flow To detect any such mass flow tomato plants grown in water culture were decapitated and placed in a canister through the lid of which the cut stem protruded and in which the pressure on the culture medium could be raised The resulting rate of exudation (flux) was measured, and compared with the flux caused by an equivalent difference in osmotic potential obtained by measuring the $\Delta $ fp of the medium and sap exuded If these values of flux were equal, movement was by diffusion alone, but if pressure caused a greater flux, an additional mass flow was indicated Preliminary experiments indicated a much greater flux in response to differences of pressure than osmotic potential, but accurate assessment of the effect was precluded by difficulties inherent in this straightforward approach A less direct technique was therefore devised; the change in flux caused by changing the osmotic potential of the external medium (the hydrostatic pressure being maintained constant) was compared with the change in flux caused by changing the external pressure (the osmotic potential of the external medium being kept constant) The changes in flux were measured in such a way as to minimize changes in the osmotic potential in the xylem and in resistances to diffusion or mass flow respectively In this way the change in flux per unit change in osmotic potential difference across the cortex (osmotic permeability coefficient, $\text{k}\_{0}$) and the change in flux per unti change in pressure difference across the cortex (pressure permeability coefficient, $\text{k}\_{p}$) could be compared under the same pressure gradient and in addition the effects of pressure gradients on $\text{k}_{0}$ could be studied Thus, the effects of a pressure gradient on the diffusional movement of water could be assessed, as well as any mass flow component of the flux detected and measured

A Liasso-Rhaetic flora in South Wales.

Abstract: A fossil flora is described from clay-filled fissures in the Carboniferous Limestone near Bridgend, South Wales. Nearly all the specimens belong to the conifer Cheirolepis muensteri. Most of them are charred fragments of various organs in which internal tissues are preserved. Cheirolepis was previously known from compressed German specimens yielding cuticles but no other tissues. The leaf is found to have a single vascular bundle and the wood is of somewhat Taxodiaceous structure but without xylem parenchyma. The bark produces thin scales of secondary phloem and cork. The male cone bears microsporophylls spirally; they are essentially dorsiventral and probably bear two pollen sacs only. The pollen is of unusual structure. The seed is orthotropous and the testa appears to be double. Other species are rare fragments of cuticle representing several Mesozoic genera and isolated spores, three of which have been determined. The age of the flora is between Rhaetic and Lower Liassic; it most resembles a flora in south-west Germany which is regarded as Lias $\alpha $. Reasons are put forward for supposing that the forest or scrub was burnt, and then the charred fragments were washed into water-courses in limestone fissures which soon after were submerged by the rising Liassic sea.

The effect of potassium on the resting metabolism of the frog's sartorius.

Abstract: Solandt, in 1936, found that the rate of heat production of a frog's sartorius at rest is greatly increased by raising the K-ion concentration in the surrounding fluid; Fenn and his colleagues (1930 to 1936) had observed a similar effect with the oxygen consumption. Solandt's findings have been confirmed and extended: (1) the enhanced heat rate is not associated with any mechanical change in the muscle; (2) when a solution with high K (oxygenated) is replaced by oxygen there is usually a large increase in the heat rate, as though something previously being removed by diffusion were accumulating near the surface; (3) with normal Ringer the threshold is at about 10mM-KCl and the full effect at about 18mM, corresponding to membrane potentials of about 65 and 50 mV respectively instead of the usual 90 mV; (4) Ca in about equimolar amounts antagonizes the action of K; (5) Rb acts like K but about twice the concentration is needed; (6) if $\text{NO}\_{3}$ or I is substituted for the Cl of Ringer the effect of K is similar but occurs at a lower concentration; (7) if sucrose is substituted for NaCl in Ringer, or $\text{SO}\_{4}$ for Cl (provided that the Ca-ion concentration is maintained by saturating with $\text{CaSO}\_{4}$), the same effect of K is observed, but with isotonic sucrose alone, or without extra Ca in the $\text{SO}\_{4}$-Ringer, a large increase of heat rate occurs without extra K; (8) in the absence of $\text{O}_{2}$ the increment of heat rate due to K is small. It is concluded that a partial depolarization of the surface of the muscle fibres (less than that required to induce contraction) can cause a limited change of internal organization which release some, but not all, of the chemical processes that are normally set in train in a coherent way by excitation. The limited reactions caused by high external K serve no useful physiological function; they are inco-ordinate parts of the normal cycles which are turned on after ordinary contraction has been started by a greater temporary depolarization. The manner in which these internal activities can be induced by a reduction of the potential difference across the surface membrane is discussed.

A study in body ballistics: seat ejection.

Abstract: Escape from high-speed aircraft has necessitated the development of ejection seats. This introduced the physiological problem of the maximum acceleration and rate of change of acceleration which can be sustained by the seated human body along the vertical axis of the spine. The ballistic behaviour of the human body has been studied by various experimental techniques. Natural frequencies and damping characteristics of the ejected system (man and seat) have been determined by subjecting the instrumented body to continuous vibrations over the frequency range from 1 to 20 c/s, and also by investigation of its response to spike- and step-force functions in sledge-hammer and seat-drop experiments. Results with different cushion and spring systems interposed between man and seat were compared and related to accelerometer records obtained from live subjects on ejection test rigs. The data derived from these experiments has been studied on an electronic servo simulator and the general physiological requirements for ejection-seat guns have been defined. Under these conditions a rate of change of acceleration of 300 g/s with a maximum peak acceleration of 25 g should be considered as limiting factors for accelerations tolerable by the body. This implies that the characteristics of the acceleration applied to the seat should be less than these figures by an amount depending on the elasticity of the cushion employed. It is suggested that the optimum duration of the thrust is approximately 0.23 s and a maximum overshoot in peak acceleration in the body would result with a rate of change of acceleration of 400 g/s applied to the seat.

A comparison of acetylcholine and stable depolarizing agents.

Abstract: The method of brief ionophoretic application was used to compare the time course of action of acetylcholine and of stable depolarizing substances. The drugs were discharged from twin micropipettes, allowing a quick comparison of two substances, applied from virtually the same point source. With pulse application at close range, the time course of an acetylcholine potential is faster than those produced by other drugs. Comparing half-times of decay, if that of the acetylcholine potential is taken as unity, carbaminoylcholine is slower by a factor of about 2, nicotine and succinylcholine by 2 to 3, and decamethonium by approximately 10. After treating the muscle with prostigmine, the average difference in time course between acetylcholine and carbachol effects becomes insignificant. Different processes are discussed whose kinetics influence the shape of the observed drug potentials.

The Experimental Induction of Gynogenesis in the Mouse. I. Irradiation of the Sperm by X-Rays

Abstract: Sperm of the mouse, Mus musculus, was X-irradiated in vitro before fertilization. Dosages were between 100 and 50 000r. With increasing irradiation of the sperm, the chromosome complement of embryos, scored at $3\frac{1}{2}$ days' gestation, declined from diploid to haploid. Higher dosages increasingly retarded embryonic development, 30 000 and 50 000r restricting development to the first cleavage. Gynogenetic development was very abortive. X-irradiation did not usually prevent male pronucleus formation or syngamy. Loss of paternal chromosomes occurred in the embryos during development, probably by the loss of chromosome fragments into sub-nuclei. After 30 000 or 50 000r, abnormal pronuclear relationships were found. In some eggs, sperm entry and the growth of the male pronucleus did not stimulate completion of the second maturation division. In other eggs, the single pronucleus was probably female, the male pronucleus having degenerated. Polyspermy occurred at the same dosage. 1000r almost completely suppressed implantation. 500r caused considerable embryonic mortality. Irradiation damage to the centriole or cytoplasm of the sperm in addition to destruction of its chromosomes may have caused the retarded development of the embryos.

The estimation of the number of histocompatibility genes controlling the successful transplantation of normal skin in mice

Abstract: The success or failure of a transplant of tissue from one animal to another depends on the action of a number of independently acting histocompatibility genes which are present in the donor9s tissues and absent from those of the host. An estimate of the number of such genes in mice can be made from the proportion of grafts which survive transplantation from either of the two parent strains to members of their F 2 generation. If n is the number of genes, the proportion of successful grafts = (¾) n . Most previous work of this sort has used tumour tissue to provide material for grafting. A normal tissue, such as skin, has several advantages over malignant tissues which may kill the host and are difficult to observe; it is also probably more exacting in its genetic requirements. We have used single 7 mm diameter full-thickness pieces of skin transplanted orthotopically to the side of the chest as test grafts. Taking survival in an autograft-like condition 100 days after grafting as the criterion for judging success or failure, two of 120 A strain and one of 154 CBA strain grafts survived transplantation to F 2 generation mice. Assuming that each separate antigen is capable of causing breakdown of the graft, these figures imply that certainly not less than fifteen independently segregating genes control the fate of a transplant. But since breakdown of such 9successful9 grafts was observed as late as 180 days after grafting, the estimates represents minimal values only. The survival times for the grafts are distributed widely from 10 or 11 days (the normal survival time for interstrain homografts) to more than 100 days. Both frequency distributions (for A and CBA donors) are quite unlike the theoretical distribution for the frequency of occurrence of 0 to 15 homozygous gene pairs in the F 2 generation. They also differ between themselves and suggest that the alleles in the CBA strain are less potent sources of antigens than those in the A strain. It is not possible to equate numbers of gene differences with survival for any given number of days, but clearly the individual genes have widely differing powers of forming antigens. The process of destruction, once begun, is soon complete and resembles the breakdown process in normal interstrain homografts more closely than it does the slower, vacillating process found in mice that have acquired tolerance to foreign skin by virtue of an inoculation during embryonic life. Second set grafts are usually thrown off more rapidly than the first set but anomalous results occur occasionally. Immunoparalysis was not found even when five sets of grafts were transplanted in succession.

Problems in the resuscitation of mammals from body temperatures below 0 degrees C.

Abstract: Two hundred and seventy-five years have passed since Robert Boyle discovered that extreme cold prevented the putrefaction of animal tissues. He found that frogs and fish actually survived for short periods when the water surrounding them had frozen, but succumbed after several days’ encasement in ice. Boyle described these as promiscuous experiments. He also reported two modes of death in humans exposed to intense cold. Usually the extremities were gradually invaded by numbness which spread over the entire body so that the individual died insensibly. By contrast, horsemen wearing armour were seized violently around the waist by the cold. It caused them unspeakable abdominal pains and other torments which continued until the subjects died from exhaustion (Boyle 1683). Boyle’s observations have since been amply confirmed, and today it is well known that cold blooded animals do not survive complete freezing of all their body water (Scholander et al . 1953). Warm blooded animals, including the hibernators, are even more sensitive to chilling. Their breathing and heart beats stop at deep body temperatures well above freezing point. The animals do not recover spontaneously when rewarmed and were therefore assumed to be dead (Adolph 1951; Lyman & Chatfield 1955). A few years ago there seemed little possibility that mammals could be resuscitated from body temperatures below 0° C, and no prospect whatsoever that the work on storing isolated mammalian cells at very low temperatures would ever be applicable to the intact animal. There were, however, reports from Russia that bats and ground squirrels had been revived from sub-zero temperatures (Kalabuchov 1934; Murigin 1937). Then we heard that Dr Andjus of the University of Belgrade had shown that rats chilled till breathing and heart beats stopped were not necessarily dead (Andjus 1951). We developed his techniques at Mill Hill so that rats and mice can now be easily revived after an hour of suspended animation at body temperatures just above zero (Andjus & Smith 1955; Andjus & Lovelock 1955; Goldzveig & Smith 1956). Meanwhile Dr Parkes and Dr Lovelock and I had found that golden hamsters survived respiratory and cardiac arrest at deep body temperatures below 0° C (Smith, Lovelock & Parkes 1954). In some animals the deep body temperature fell as low as –5° C without the formation of ice in any of the tissues. These supercooled hamsters were readily resuscitated and recovered fully. Others froze progressively until, when the internal temperature had been below freezing point for 1 h, they were rigid and, when supported only by the neck and tail, would uphold an additional load equivalent to their own body weight of 100 g. Such animals were completely re-animated by warming the whole body with diathermy and simultaneously giving artificial respiration. The skin and superficial tissues contained large quantities of ice. Nevertheless, the extremities showed no signs of frostbite unless they had been forcibly bent when frozen (Smith 1954). The eyes, which were sometimes clouded for a short while after thawing, usually cleared completely, although occasionally lens opacities developed later. Ice crystals were also present in the brain and internal organs. Calorimetry suggested that as much as 50% of the body water had frozen in some animals which recovered fully. This work, which was reported last year (Smith 1956 a, b ; Lovelock & Smith 1956) has raised many problems. Some of these problems arose when we tried to repeat the experiments on larger mammals.

The Cytochrome System of the Cecropia Silkworm. II. Spectrophotometric Studies of Oxidative Enzyme Systems in the Wing Epithelium

Abstract: As shown by spectroscopic studies, the wing epithelium of the Cecropia silkworm is typical of the insect9s non-muscular tissues in undergoing a virtual breakdown of the cytochrome system at the outset of pupal diapause, and a prominent resynthesis of this system when diapause is terminated. Further information on these marked changes has now been provided by spectrophotometric determinations of DPNH oxidase, succinate-cytochrome c reductase, DPNH-cytochrome c reductase, and cytochrome c oxidase activities in particulate preparations from wing homogenates. By the measurement of these activities, the changing concentrations of cytochromes c, b, $\text{b}_{5}$ and $\text{a + a}_{3}$, respectively, have been followed during the course of metamorphosis. In the freshly pupated insect, all the cytochrome components are present in high concentration. However, during the next 24 h the wing loses all but a trace of its cytochrome system; cytochromes b and c decline in concentration by more than 95% and, by present techniques, thus reach undetectable levels which then persist throughout diapause. Cytochromes $\text{b}_{5}$$\text{and a + a}_{3}$ also decrease prominently, but to a lesser degree, and low concentrations of both components remain detectable in the diapausing wings. Several months later, when the insect9s prothoracic glands function to terminate diapause, cytochromes b and c reappear in detectable concentration. During the subsequent growth and development of the adult moth, b and c, together with $\text{a + a}_{3}$$\text{and b}_{5}$, once again return to a high level. These findings confirm the results of the earlier, spectroscopic studies, afford a quantitative insight, and provide an explanation for several metabolic peculiarities of the diapausing tissues, particularly their extremely low respiration and the virtual insensitivity of this respiration to cyanide or carbon monoxide. In addition, the present findings strongly support the view that cytochrome synthesis in Cecropia and its relatives is closely linked to the action of the prothoracic gland hormone. According to the present analysis, withdrawal of this endocrine support for growth at the outset of diapause is causally related to the breakdown of the cytochrome system. And when the endocrine organs recover their function to bring about the termination of diapause, resynthesis of the cytochrome system appears to represent at least one type of reaction which intervenes between the primary action of the prothoracic gland hormone and the insect9s developmental response.

The cytochrome system of the Cecropia silkworm. I. Spectroscopic studies of individual tissues

Abstract: Except in the somatic muscles (which throughout metamorphosis retain a classical cytochrome system in high concentration), the cytochrome system of the Cecropia silkworm is known to undergo marked changes during the course of metamorphosis, especially in relation to the onset and termination of the pupal diapause. These changes have now been studied in individual tissues and organs by the technique of low-temperature spectroscopy. The larval tissues contain a complete cytochrome system including moderate to high concentrations of cytochromes $\text{a + a}_{3}$, b, c and $\text{b}_{5}$. By contrast, the tissues of the diapausing pupa show a seemingly incomplete cytochrome system in that components b and c are not detectable; cytochromes $\text{a + a}_{3}$ and $\text{b}_{5}$ persist in low though still detectable concentration. Consequently, the onset of pupal diapause is accompanied by a generalized decrease in concentration of the several cytochromes, including the virtual disappearance of b and c. Several months later, when the insect9s prothoracic glands function to terminate diapause, cytochromes b and c promptly reappear and, together with $\text{a + a}_{3}$ and $\text{b}_{5}$, then undergo a progressive increase in concentration during adult development. The net result is that the post-diapausing tissues are re-equipped with a normal cytochrome system. In view of the intracellular localization of cytochromes $\text{a + a}_{3}$, b and c in mitochondria, and that of $\text{b}_{5}$ in the endoplasmic reticulum, the results of the present study implicate prominent alterations in these organelles during the course of metamorphosis. And, since the growth and development of the post-diapausing insect are known to require the renewed presence and function of a normal cytochrome system, the resynthesis of this system at the termination of diapause is evidently closely linked to the action of the prothoracic gland hormone.

Experimental Studies in Insect Parasitism. X. The Reactions of some Endopterygote Insects to an Alien Parasite

Abstract: Eggs of an ichneumon fly, Nemeritis canescens , have been injected into endopterygote insects to which this parasite was alien. In larvae, pupae and adults of Tenebrio molitor (Coleoptera) almost all the eggs hatched; and within 24 h haemocytes enveloped the parasite larvae and melanin was deposited over their mouth and anus. The pattern of these reactions was the same in all cases and at all stages. When individuals of Tenebrio were given repeated injections at weekly intervals, they reacted to the last parasite exactly as to a first. Female individuals that had been repeatedly injected were allowed to develop and to lay eggs; when larvae reared from those eggs were injected they made the same characteristic reactions. No trace of increased tolerance or resistance on the part of Tenebrio was observed in either experiment. Larvae and pupae of Diataraxia oleracea (Lepidoptera) rapidly encapsulated parasites injected into them; adults made no visible reaction. Nemeritis larvae fed, grew and ecdysed in these adults, and only the premature death of the moth prevented the parasite’s development. In feeding larvae, resting larvae and adults of Calliphora erythrocephala (Diptera), the haemocytic and melanin reactions to injected parasites were both weak; in pupae the haemocytic reaction was weak but the melanin reaction strong. In the adult blowflies, parasite larvae lived as long as 7 days, but did not grow and seemed unable to use the food they had ingested. Observations recorded in this and the two preceding papers of the series are compared and discussed. The haemocytic reaction to Nemeritis , as observed in several orders of insects, is a true defence reaction and, when strong enough, leads to the death of the parasite. Deposition of melanin acts as a defence reaction only fortuitously, when the deposit is so sited as to prevent a vital activity, such as the hatching or the feeding, of the parasite. The reactions to Nemeritis of the different kinds of hosts so far investigated are distinguishable, but no constant difference has been observed that would serve to distinguish the reactions of exopterygote from those of endopterygote insects.