Showing papers in "Proceedings of The Royal Society B: Biological Sciences in 1961"

A Theory of Drug Action Based on the Rate of Drug-Receptor Combination

Abstract: A theory of drug action is developed on the assumption that excitation by a stimulant drug is proportional to the rate of drug-receptor combination, rather than to the proportion of receptors occupied by the drug. The properties of a drug can then be specified by two rate constants: k$_{1}$, the association rate constant, and k$_{2}$, the dissociation rate constant; the ratio k$_{2}$/k$_{1}$ = k$_{e}$ corresponds to the reciprocal of the 9affinity9. The value of k$_{e}$ then determines potency, and k$_{2}$ determines whether the drug is a powerful stimulant (k$_{2}$ high), a partial agonist with ability both to excite and to antagonize (k$_{2}$ moderate) or an antagonist with vestiges of stimulant action (k$_{2}$ low). Qualitatively such a theory accounts for the persistence of effect of an antagonist on a tissue; for the characteristic sequence of excitation followed by block with drugs such as nicotine; for certain forms of tachyphylaxis; and for the vestiges of stimulant action possessed by classical antagonists. The theory has been tested on the guinea-pig ileum with acetylcholine and histamine as agonists, hyoscine, mepyramine and atropine as antagonists and alkyltrimethylammonium compounds as partial agonists, and it was corroborated in the following respects: 1. The dose-response curve of acetylcholine or histamine has the predicted form, if it is determined with an auxotonic rather than with an isotonic lever. 2. The rates of offset and of onset of antagonism, expressed in terms of change of receptor occupation by the antagonist, follow an exponential course from which k$_{1}$ and k$_{2}$ can be measured. Values of k$_{2}$/k$_{1}$ so obtained agree with those obtained from the intensity of antagonism at equilibrium. The rate of onset of action increases in proportion to the antagonistic dose ratio finally achieved. The rate of offset of action is independent of the intensity of the antagonism or of the time taken to achieve it, up to dose ratios of 20 to 100. Diffusion barriers do not appear to contribute significantly to the time course of action of drugs such as hyoscine or mepyramine except at high dosage. 3. With the alkyltrimethylammonium compounds (hexyl to dodecyl): (a) the rate of onset and offset of antagonistic action fell with increasing potency. (b) The excitation produced always reached a peak response soon after injection which faded thereafter to a lower equilibrium value, with a time constant comparable with that predicted from the atropinic action. The rate and proportion of fade increased with dose. The dose-response curve for peak responses is bell-shaped, but not that for equilibrium responses. (c) The slope of the foot of the dose-response curves of the series and the magnitude of the maximum equilibrium responses correlated with the estimates of k$_{1}$ and k$_{2}$, respectively, obtained from analysis of the atropinic action. The alkyltrimethylammonium compounds could be specified by a k$_{1}$ which is constant and a k$_{2}$ diminishing by a factor of about 2$\cdots $5 for each methylene group added. It is suggested that association is determined by the cationic head, and dissociation by shorter-range binding forces. 4. The responses to strong stimulants, such as histamine or acetylcholine, cannot be fully described in these terms. Following exposure to them the ileum is non-specifically desensitized. This desensitization is detectable with small doses, increases with dose and duration of exposure, and differs in its course to recovery from a specific antagonism. 5. A similar desensitization follows the removal of potassium from the fluid in which the ileum is immersed, and the two forms of desensitization summate. If potassium-free solution is applied rapidly, a contraction of the ileum occurs, indistinguishable from that due to acetylcholine. It is suggested as a working hypothesis of stimulant action that the drug ion exchanges with potassium at the receptor, and is then released from the receptor in exchange for potassium derived intracellularly, so that the chemoceptive action involves an extraction of potassium from the tissue. The implications of rate theory and of non-specific desensitization for theories of drug action are discussed.

The Functional Organization of the Brain of the Cuttlefish Sepia officinalis

Abstract: The functional organization of the brain of Sepia has been investigated by electrical stimulation. As a result several new divisions of the brain have been made. The pedal ganglion has been shown to consist of four parts: (1) the anterior chromatophore lobes innervating the skin and muscles of the anterior part of the head and arms; (2) the anterior pedal lobe innervating the arms and tentacles; (3) the posterior pedal lobe innervating the funnel, collar and retractor muscles of the head; (4) the lateral pedal lobes innervating the muscles of the eyes and tissues of the orbits. The palliovisceral (or visceral) ganglion, apart from the magnocellular lobe demonstrated by Young (1939), is shown here to consist of (1) a central palliovisceral lobe innervating the mantle, funnel and viscera; (2) a pair of lobes innervating the muscles of the fins; (3) a pair of posterior chromatophore lobes innervating the muscles of the chromatophores and skin of the mantle, fin and back of the head; (4) a pair of vasomotor lobes. Because of these new divisions the three main groupings of the suboesophageal neural tissue are now referred to as the anterior, middle and posterior suboesophageal masses corresponding to the old brachial, pedal and palliovisceral divisions. The suboesophageal centres are classified as lower motor centres and intermediate motor centres, depending on the kind of response they give to electrical stimulation and their peripheral connexions. In the supraoesophageal lobes, higher motor centres and silent areas are recognized. The silent areas include the vertical, superior frontal, subvertical, precommissural and dorsal basal lobes. Of the higher motor centres the anterior basal lobe is primarily concerned with the positioning of the head, arms and eyes, particularly during movements involving changes in direction while swimming. Such manoeuvres are brought about by the anterior basal lobe control over the fins and position of the funnel. The posterior basal lobe is here shown to consist of six main divisions: (1) the subvertical lobe; (2) the dorsal basal lobes; (3) the precommissural lobe; (4) the medial basal lobe; (5) the lateral basal lobe; (6) the interbasal lobe. The medial, lateral and interbasal lobes are higher motor centres. The lateral and medial basal lobes control movements of the chromatophores and skin; the medial basal lobe controls swimming, breathing, fin movements and various visceral functions. The interbasal lobe controls the movements of the tentacles. The optic nerves and the optic lobes, at their periphery, are electrically inexcitable. Electrical stimulation of the centre of the optic lobes evokes all the responses that can be obtained from the other higher motor centres. The results are discussed in terms of Sanders & Young's (1940) physiological classification of the brain. A further category intermediate motor centre is recognized. Summary lists of the responses of each lobe are given on pages 516, 520, 525.

The chemical acceleration of the maturation process and its hormonal control in the male of the desert locust

Abstract: The gregarious male of the desert locust shows a characteristic colour change during adult life; it is light brown and pink when immature, and bright yellow when mature A mature, yellow male is able to accelerate the maturation process of young locusts by secreting a volatile substance which is produced in the epidermis and transmitted to the recipients by olfaction through the antennae and by contact over the body surface The presence of this lipophilic substance is indicated by a vibration reaction, in which antennae, palpi and hind femora take part (Loher 1959) The volatile material can be extracted and preserved in oil and fat solvents Extirpation and implantation of the corpora allata have demonstrated that in the male these endocrine glands are in control of sexual maturation and some associated processes, such as the production of the epidermal secretory substance, the colour change, the development of the accessory glands and the acceleration of maturation which results from wounding The possibilities of combined action between the corpora allata and the epidermal secretory substance are discussed

The induction of sporulation in mould fungi

Abstract: Sporulation of Penicillium griseofulvum is rapidly induced in submerged conditions when mycelium is placed in a medium containing a high concentration of glucose but without assimilable nitrogen. External Mg$^{2+}$, K$^{+}$, PO$\_{4}^{3-}$ are required for sporulation. In these conditions the induction of sporulation is completed in 3 to 4 h, before there is any sign of conidiophore formation. The high concentration of glucose required for sporing can be effectively replaced by an equivalent concentration of non-assimilable sugars (sorbose, D-arabinose) provided a small amount of glucose is present to supply the energy requirements of the fungus. High concentrations of salts are not effective and tend to inhibit sporing. Induction of sporing in submerged conditions is inhibited by certain concentrations of ascorbate, Hg$^{2+}$, cetyltrimethylammonium bromide and 3,4-dichlorphenylserine which do not affect vegetative growth. The most powerful stimulus to sporulation in Penicillia and other fungi comes from emergence of mycelium from submerged into aerial conditions. Experiments with P. griseofulvum and P. chrysogenum show that emergence of the mycelium causes a sharp change in physiological behaviour which is manifest before any morphogenetic changes are apparent. Aerial mycelium assimilates NH$\_{4}^{+}$ in the complete absence of external carbohydrate, whereas submerged mycelium will not assimilate NH$\_{4}^{+}$ in these conditions even when fully aerated. The aerial stimulus is not associated with the supply of O$\_{2}$ nor with concentration of CO$_{2}$ nor with water loss from the mycelium. Evidence from three independent methods of investigation points to the occurrence of an abrupt change in the physical condition of the cell surface when mycelium emerges from a liquid medium into the air. Each method indicates a physical change which takes place within a few seconds of emergence, which increases slowly with time in aerial conditions, and which, like aerial sporulation itself, is reversed or delayed by re-wetting. It is considered that the primary aerial stimulus to sporulation is associated with some physical change at the cell surface caused by the abrupt formation of an air/water interface.

Stress and adrenaline in relation to the diurnal cycle of epidermal mitotic activity in adult male mice.

Abstract: With mice starved to the point at which epidermal mitotic activity had almost ceased, a study has been made of the subsequent recovery of mitotic activity in vitro , using a simple phosphate-buffered saline medium. The results obtained suggest that the suppression of epidermal mitotic activity during starvation is due primarily to the increasing concentration of a mitotic inhibitor. It is suggested that this inhibitor is adrenaline secreted in excess during the stress of starvation. After both starvation and adrenaline treatment mitotic activity recovers rapidly when the skin is separated and placed in a saline medium, even when no nutrients are present. Further it is evident in both cases that during the course of the inhibition epidermal cells continue to prepare for division so that, when the inhibitor is washed out, mitoses appear in abnormally large numbers. It was also found that adrenalectomy is followed by a considerable rise in the epidermal mitotic rate and by the elimination of the diurnal mitotic rhythm. It is suggested that this rhythm is normally based on the hour-by-hour variations in the rate of adrenaline secretion. A mouse when awake and active evidently has a raised adrenaline blood content and thus a low epidermal mitotic rate; a mouse when asleep or resting has a reduced adrenaline blood content and thus a high epidermal mitotic rate. The epidermal mitoses developing when a mouse sleeps are partly those for which preparation was made when the mouse was awake and partly those which then complete their preparation. Thus it is possible to show that the longer a mouse remains awake the higher is the number of epidermal mitoses subsequently developing.

The Structure of the Muscle Fibres in the Translucent Part of the Adductor of the Oyster Crassostrea angulata

Abstract: The arrangement of the protein filaments and other details of the ultrastructure of the contractile apparatus have been studied by methods which include the examination of thin sections in the electron microscope. The results help towards a better understanding of three general problems: the reasons why some muscles appear striated and others smooth; the mechanism of contraction in muscles which are not cross-striated; and the mechanism by which certain muscles of molluscs can maintain a high level of tension for long periods without fatigue. The filaments are of two kinds, thick paramyosin filaments, and much thinner filaments which very probably contain mainly actin. Both are short, relative to the length of the fibre, lie parallel to the fibre axis, and are grouped into separate arrays which alternate with each other along the length of the fibre. The arrays partly overlap, and in the regions of overlap each thick filament is surrounded by twelve thin ones, and each thin filament is usually 'shared' by two thick ones. The regions of the fibre where the arrays of thin filaments are exposed are identified as I-bands, the intervening regions (arrays of paramyosin filaments partly overlapping with arrays of thin filaments) as A-bands. The relative positions of the arrays change with the length of the muscle: the extent of overlap in the A-bands increases as the muscle shortens and decreases on stretching. Thus the muscle shortens by a sliding filament mechanism. Although the muscle is identified as a striated muscle because it has A- and I-bands, it differs from cross-striated muscles in two respects. In the first place, the bands lie at a small angle (about 10 degrees) to the fibre axis, and are arranged helically around the outer part of the fibre, giving rise to the 'double-oblique striation' visible in the light microscope; moreover, the bands branch and anastomose with each other in the core of the fibre. In the second place, there are no Z-lines, but in the planes where Z-lines would be expected, discrete dense-bodies are present. Similar dense-bodies occur in many smooth muscles, for example, in the mammalian uterus (Mark 1956; Shoenberg 1958), and in the anterior byssus retractor of Mytilus (Hanson & Lowy 1959a). The contractile apparatus of the latter closely resembles that of the oyster muscle in many respects, but the filaments are not clearly grouped into separate arrays. This feature, the presence or absence of segregated arrays of filaments, could serve as the main criterion for distinguishing striated from smooth muscles. Where the arrays of thick and thin filaments overlap in the A-bands, the two kinds of filaments appear to be cross-linked by means of transverse projections which belong to the thick filaments. The view is put forward that the paramyosin filaments are comparable to the myosin-containing filaments of the cross-striated muscles of vertebrates, and that the cross-links in the oyster muscle are comparable to actin-myosin links. The role which paramyosin filaments play in the mechanism by which certain muscles of molluses maintain tension very economically is also discussed. The results described in this paper support the hypothesis (Lowy & Millman 1959b, 1960) that tension is held by cross-links in a sliding filament contractile mechanism and that the economy of the system is due to a low rate of detachment of these cross-links. The alternative 'catch'-mechanism hypothesis (Johnson, Kahn & Szent-Gyorgyi 1959; Johnson & Szent-Gyorgyi 1959; Ruegg 1959) which supposes that tension is maintained by some change of state of the protein within a paramyosin system, is difficult to reconcile with the present findings. Structures which resemble the 'dyads' of the cross-striated muscles of vertebrates have been found beneath the cell membrane. Their possible function in the intracellular transmission of stimuli is discussed in view of the fact that the fibres of the oyster muscle are only about 2 $\mu $ thick.

Rheotaxis of Spermatozoa

Abstract: 1. The response of human and bull spermatozoa to vertical velocity gradients has been examined, the fluid flow being in horizontal planes. 2. Dead human and bull spermatozoa point downstream (negative rheotaxis) in the top half of a parabolic velocity gradient and upstream (positive rheotaxis) in the bottom half. Although spermatozoa point preferentially in one or other direction, parallel to the stream ­ lines, in linear velocity gradients, this cannot be described as positive or negative rheotaxis because the direction in which the spermatozoa point is determined by the direction of shear. 3. The response of dead human and bull spermatozoa to velocity gradients is due to the head of the spermatozoon having a higher specific gravity than the tail, which causes the spermatozoon to sink head first in a medium of lower specific gravity than that of the spermatozoon. 4. Live human and bull spermatozoa exhibit positive rheotaxis, i.e. they swim up stream, in both halves of a parabolic velocity gradient. 5. The behaviour of previously flow-orientated spermatozoa in a just-reversed velocity gradient has been photographed and analysed. Though the mechanism whereby dead spermatozoa re-orientate in such conditions is understood, live spermatozoa, which also re-orientate in these conditions, may do so by a different and, at present, unknown mechanism.

Synaptic structure and its alteration with environmental temperature: a study by light and electron microscopy of the central nervous system of lizards

Abstract: Three types of structural change can be produced in the nervous system of lizards by altering the environmental temperature from 19 to 32°C. These changes are reversible and take from 1 to 4 weeks to occur. (1) In the nucleus sphericus the fibre plexus within the zone of cells becomes filled with argyrophilic spheres, 2 to 3 μ in diameter, when the animals are kept at the higher temperature. (2) In the cochlear grey, the superior olivary nucleus and the hippocampus there is a loss of neurofibrillar rings when the animals are kept at the higher temperature. This is accompanied by: (3) a loss of mitochondrial material. Electron microscopical studies show that both these last changes occur in synaptic terminals. Within the terminal bags neurofilaments can be seen orientated in the form of a ring, encircling a dense group of mitochondria. Around the neurofilaments is a zone of pale-staining cytoplasm, which is free from synaptic vesicles. The classical neurofibrillar boutons are seen in the regions that show neurofilaments in electron micrographs. Regions that show no neurofibrillar boutons appear to be free of terminal neurofilaments.

Production of a New Lysergic Acid Derivative in Submerged Culture by a Strain of Claviceps paspali Stevens & Hall

Abstract: 1. The production of a new lysergic acid derivative, identified as D-lysergic acid $\alpha $-hydroxyethylamide, in submerged culture and in yields up to 1 mg/ml. and above, by a strain of Claviceps paspali Stevens & Hall is reported; this substance can be converted in high yields into D-lysergic acid amide. 2. The morphological properties of this strain under different culture conditions are examined and it is shown that it grows in a form resembling natural sclerotia. 3. The biochemical culture conditions for the production of the new lysergic acid derivative in shake flasks and in stirred fermenters, the course of the fermentation, the methods for the isolation and purification of the substance and its transformation products and some of its chemical and physical properties are described.

The Croonian Lecture: Radiocarbon Dating and Quaternary History in Britain

Abstract: The lecture is an attempt to show the way in which research upon the Quaternary Period in Britain is being affected by the application to it of radiocarbon dating. Mild interstadial periods during the last glaciation can be distinguished, set in sequence and related to similar European interstadials. It is shown that a brief climatic oscillation occurs widely in the Late-glacial transition from Full-glacial to Post-glacial time, and that the vegetational changes registered in pollen zonations of the Post-glacial Period are to some degree synchronous. They reflect widespread climatic changes, as do major horizons in bog stratigraphy that can also be correlated by radiocarbon dating. The method has a most powerful application to archaeology and it promises some resolution of the complex interaction of eustatic, isostatic and tectonic factors that have affected those relative movements of land and sea level recorded by the submerged forests, estuarine formations and raised beaches of the British Isles. Between the results of British Quaternary study in these and other fields there is developing considerable consistency of pattern, as also between British Quaternary History and that of other parts of the world.

Changes of Oxygen Tension in Brain and Somatic Tissues Induced by Vasodilator and Vasoconstrictor Drugs

Abstract: Oxygen tensions in hypothalamus, cerebral cortex, muscle, testis and subcutaneous tissue of anaesthetized rats were measured quantitatively by the oxygen-cathode technique. The resting levels of oxygen tension and the response to breathing oxygen were assessed and then vasodilator or vasoconstrictor drugs were injected and the changes of oxygen tension were observed. 5HT (Serotonin) caused marked falls of oxygen tension in brain, muscle, testis and subcutaneous tissues, lasting 1 to 2 h, when given by intraperitoneal injection (i.p.) and profound but transient falls when given intravenously (i.v.). Noradrenaline (i.v.) caused a rapid transient rise of oxygen tension in brain, a transient fall in muscle, a longer fall in testis, and a variable response in subcutaneous tissue. Reserpine (i.v.) was followed by a slow fall in oxygen tension in brain especially if the body temperature was allowed to fall. (Alone a fall of body temperature tended to increase the oxygen tension in brain.) Amphetamine (i.v. or i.p.) increased the oxygen tension in brain. The mono-amine oxidase inhibitor, tranylcypromine (SKF 385) caused a steady rise of oxygen tension in all tissues studies except testis. The subsequent (i.v.) injection of reserpine caused a rapid, marked increase of oxygen tension in brain. The oxygen tension in muscle fell, in subcutaneous tissue there was a rise followed by a fall which persisted.

6-Aminopenicillanic acid. III. Isolation and purification.

Abstract: Methods are described for the isolation of pure crystalline 6-aminopenicillanic acid from penicillin fermentation broth. With low potency fermentation broth it was found to be convenient to prepare a concentrate of the clarified broth before proceeding with other extraction methods. Negligible amounts of 6-aminopenicillanic acid could be extracted directly into organic solvents such as butanol or butyl acetate. Partial purification could be achieved by adsorption and elution from alumina and charcoal. Adsorption and elution from a suitable ion exchange resin proved more effective. Crystalline 6-aminopenicillanic acid was then obtained by concentration of this ion exchange eluate and pH adjustment to the point of minimum solubility. Alternatively, further purification of the ion exchange eluate could be achieved by chromatography on a column of cellulose before proceeding with the crystallization step. Some properties of the isolated 6-aminopenicillanic acid are also given.

Cell Wall Organization and Wall Growth in the Filamentous Green Algae Cladophora and Chaetomorpha. I. The Basic Structure and Its Formation

Abstract: This is the first of two papers dealing with the wall structure and growth of Chaetomorpha (Ch. melagonium and Ch. princeps) and of Cladophora (Cl. prolifera and Cl. rupestris). Here the structure is investigated of the side walls and cross-walls of the cells in the filaments, including the apical cells, using polarization microscopy, X-ray diffraction analysis and electron microscopy. All the side walls are finely lamellated, with microfibrils lying almost transversely and almost longitudinally, crossing each other at an angle rather less than a right angle. In Cl. prolifera, in Ch. princeps and, very rarely, in Cladophora rupestris, there is also a third set of microfibrils the direction of which lies in the obtuse angle between the other two. All three sets of microfibrils lie in spirals round the cells and, wherever all three occur, they are deposited by the cytoplasm in the same order: slow, steep, third. The signs of the spirals are constant within a species. The structure of the side walls of all four species-and of the walls of Valonia ventricosa in which the same order of deposition has been found-can be simply related on a grid of three sets of intersecting lines. In newly deposited lamellae the microfibrils irrespective of their orientation show the same considerable angular dispersion about their common direction. Further in the wall, the microfibrils of the steep set are more nearly parallel to each other and of the slow and third set more dispersed. This change is associated with cell extension. The microfibrils of each type of lamella are interwoven within and between lamellae. The microfibrils in the cross-walls, the lamellae of which are continuous with those of the side walls, lie at random, with a tendency near the edge to run parallel and perpendicular to it. In apical cells of Cl. prolifera all three sets of microfibrils pass completely over the growing apex through a random patch at the extreme tip. All three sets are more disoriented, and more widely spaced, in outer than in inner lamellae. The special features of wall deposition consequent upon plasmolysis and subsequent recovery and upon preparation for the release of swarmers are reported upon. Both cases involve the deposition of randomly oriented microfibrils. On plasmolysis cytoplasmic material is left behind on the wall, associated with new microfibrils, and some microfibrils in process of deposition are drawn away from the wall on the surface of the cytoplasm. It is concluded that in these species the cellulose microfibrils are produced by end synthesis and are oriented by a mechanism occupying a thickness of about 500 angstrom which can orient them in any one of three directions simultaneously. Wall stresses are of no significance in initial orientation. The incrusting substances continue to aggregate within the wall so that in formalin-fixed material only the outer lamellae are firmly bound together.

Effect of the Graft-Versus-Host Reaction on the Immunological Responsiveness of the Mouse

Abstract: Graft-versus-host reaction has been induced in unirradiated adult ( C 57 BL x CBA ) F 1 hybrid mice by intravenous injection of parent-line spleen cells, and the capacity of the injected animals to react to first-set and second-set grafts of A -line skin, and to Salm. typhi H antigen, has been investigated. Injection of CBA cells resulted in little or no loss of weight, a low mortality, little or no impairment of the recipient’s capacity to react to A skin or to the bacterial antigen when encountered for the first time, and no loss of pre-existing immunity to A skin. Injection of (40 to 100) x 10 6 C 57 BL cells on the other hand resulted in severe loss of weight and diarrhoea, often culminating in death. Surviving non-immunized animals reacted feebly to the bacterial antigen and some were slower than normal in rejecting first-set grafts of A skin. Pre-existing immunity to A skin was lost except in the special case when the spleen cell donor had itself been immunized against A skin. It is concluded that severe graft-versus-host reaction depresses the host’s immunological reactivity, but that the foreign cells may enable the host to muster a variety of immunological reactions by proxy.

The Response of the Sea Anemone Calliactis parasitica to Shells of the Hermit Crab Pagurus bernhardus

Abstract: The five stages in the behaviour pattern by which Calliactis parasitica transfers to shells of Buccinum, normally occupied by Pagurus bernhardus, are described. The first of these, the clinging of tentacles to shell, is a trigger for the pattern as a whole; it occurs in Calliactis already settled on glass or plastic, and more consistently, in Calliactis whose pedal disks are unattached. Tests on the frequency and speed of the clinging response under various conditions gave this information: (a) individual shells used by Pagurus vary greatly in potency; (b) Calliactis cling to shells of Pecten and Mytilus, but only erratically and after long delays; (c) Buccinum shells that have never been occupied by crabs, evoke the clinging response most consistently and rapidly; (d) removal of periostracum from Buccinum shells reduces, but does not abolish, clinging, though Calliactis responds to isolated strips of periostracum as to a shell; (e) Calliactis does not cling to dummy shells, to shells boiled in alkali, or to shells coated with a thin plastic layer; (f) Calliactis does not cling to inactivated shells when these are re-occupied by crabs. It is concluded that the clinging response depends entirely on a general molluscan shell-factor. In the settlement of the foot on the shell (the fourth stage of the behaviour pattern), a specific response to shell-factor is also involved. Vertical incisions, even complete bisection, do not abolish clinging but merely slow down the orderly pattern of the transfer to a shell. Horizontal incisions impair the pattern more. Complete horizontal section, including removal of the pedal disk alone, abolishes the clinging response and the whole behaviour pattern. Interposed stimuli show features consistent with a 5-stage programme in which the completion of each stage is a trigger for the next. But each stage may be greatly prolonged, and, if interrupted, starts again. The neuromuscular links required to co-ordinate this behaviour pattern are listed and discussed.

Long-term effects of a single whole-body exposure of mice to ionizing radiations - II. Causes of death

Abstract: The causes of death in mice exposed at the age of 30 days to a single whole-body dose of 15 MeV X-rays have been analyzed from the point of view of both percentage incidence and distribution in time. Ten groups of death causes were used, based on post-mortem findings. In the lower dose groups (50 to 457 r), the percentage incidence was found, in most cases, to vary very little with dose, but some diseases, e. g. leukaemia, did show a definite increase, and others, e. g. pulmonary tumours, a definite decrease with increasing dose. The changes in incidence were linearly related to the dose. The analysis of survival curves for each cause of death separately has revealed that while all causes were advanced by radiation, some were advanced more than others. A definite correlation was found between the acceleration of a given cause of death and the rate of change of the percentage incidence with dose. This suggests that the change of incidence is merely the result of the changed times of onset of disease; an actuarial correction has confirmed this suggestion. It is concluded that the probability of any one disease occurring remains the same in irradiated as in the control animals, the main effect of the radiation being an advancement, at different rates, of all causes of death. The age of the animal at irradiation may be an important factor in deter­mining the relative acceleration of the different diseases. In the high dose groups (549 to 780 r) a definite decrease in incidence of neoplastic diseases has been established. This may be due to a 4 9radiotherapeutic’ effect in cells which later in life might have become manifest as neoplasms.

Long-Term Effects of a Single Whole-Body Exposure of Mice to Ionizing Radiations. I. Life-Shortening

Abstract: A systematic study has been made of the reduction of life span in mice exposed to a single whole-body dose of 15 MeV X-rays. 4604 mice of an inbred A substrain were used, all of the same age, 30 days, when irradiated. Nine dose groups, from 50 to 780 r, were used, with a large number of control mice, which were kept to the end of their lives under the same conditions as the irradiated animals. An analysis of the survival curves has revealed two effects of radiation: a reduction in the median age and an increase in standard deviation of the distribution of ages at death. The latter was found to be a quadratic function of dose and it is suggested that the increase is the result of the larger spread in the ages of onset of diseases in irradiated animals. The reduction of life span was found to be proportional to dose, with no threshold. It amounts to 5∙66 ± 0∙18 weeks per 100 r, or to 38 % of the median life span for a dose equal to the LD 50 (698 r). The difference between the life-shortening in males and females was not statistically significant. The data have also been analyzed in terms of Gompertz plots and it was found that they cannot be represented by straight lines, although the displacement of the curves caused by radiation is roughly proportional to dose. The fact that after correcting for the change in standard deviation, all survival curves are parallel to each other, suggests that the effect of exposure is to ‘age9 the animal, by the removal of a few weeks of its early life.

Factors Governing the Changes in Strength of a Partially Inborn Response, as Shown by the Mobbing Behaviour of the Chaffinch (Fringilla coelebs). III. The Interaction of Short-Term and Long-Term Incremental and Decremental Effects

Abstract: When a chaffinch is shown a predator, the response (as indicated by the chink calls) increases for the first few minutes, and then slowly wanes. Some recovery occurs during about the first 30 min after the stimulus is removed, but it then virtually ceases. This suggests that two groups of processes are involved in the waning, one producing temporary effects, and the other more permanent ones. The experiments reported here were aimed at a further analysis of these processes. Two stimuli (a stuffed owl and a toy dog) were presented in all possible combinations (dog-dog, owl-owl, owl-dog and dog-owl) to wild-caught chaffinches. The lengths of the initial presentation and the rest interval were varied. The effects of the first presentation on four parameters of the second response were assessed in each case. The four parameters were the latency, the number of calls in the first 6 min, the minute in which the maximum number of calls occurred, and a measure of the rate at which the response waned. Owl was found to be a stronger stimulus than dog, but the relations between the various response characteristics were similar for both stimuli. For every stimulus sequence, the number of calls given in a second presentation after a long rest interval was smaller than the number given to the same stimulus by experimentally naive birds. The decrement was greater in sequences where the same stimulus was repeated, the stimulus-specificity increasing with the length of the initial presentation. Increase in the length of the initial presentation resulted in a progressive decrease in the second response with owl-owl and dog-dog sequences, but an increase with the owl-dog sequence. The interrelations between the response characteristics were different on second presentations after a long rest interval from those found for initial responses. In particular, the latency decreased although the number of calls also decreased. The results can be understood in terms of an interaction between long-term incremental and decremental effects. The evidence for the incremental effect comes from three independent sources—from the changes in latency, from the increase in the response to dog presented 24 h after owl with lengthening of the initial presentation, and from some additional experiments with owl models. With short rest intervals the response decrement was greater than with long ones, and was also different in kind (as indicated by differences in the relations between the response charac­teristics). There was no clear evidence that the short-term effects were stimulus-specific. Here again there appear to be incremental effects interacting with the decremental ones, the evidence for the former coming from the initial warming up phase of all responses, irregulari­ties in the recovery curves, and additional experiments with a very short initial presentation. It is concluded that concepts like habituation, extinction, adaptation and fatigue, while useful in a descriptive sense, must not be taken to imply a unitary underlying process.

Foetal Growth in the Mouse

Abstract: In polytocous mammals an inverse relation is known to exist between the number of young in the litter and the size of the young at birth. It has been customary to attribute this to prenatal competition for a limited pool of nutrients in the maternal circulation (Hammond & Marshall 1952). The present study was undertaken in order to subject the traditional theory to quantitative test. Pregnant mice were killed shortly before term and their foetuses were weighed. Some of the pregnancies had resulted from natural ovulation. Others were obtained by inducing superovulation with hormone treatment, in some cases in adult, and in others in sexually immature females. Analysis of the foetal weights yielded a number of results at variance with the predictions of the theory of competition, notably the following: (1) Foetal growth was more affected by the presence of other foetuses if these w9ere in the same, rather than in the opposite, uterine horn. (2) Foetuses dying in mid-pregnancy, when their nutritional demands would still be small, exerted effects upon the growth of the survivors comparable to those exerted by foetuses surviving the middle period. (3) The signs of nutritional stress exhibited by sexually immature females carrying abnormally large numbers of foetuses, were not accompanied by a reduction in foetal weight after due allowance for foetal number. (4) The foetus occupying the top (ovarian) position in the uterine horn was on average significantly lighter than its neighbour. These results can be better accommodated by an alternative theory of foetal growth (Eckstein, McKeown & Record 1955) which proposes that the chief regulating factor is the pressure at which maternal blood is supplied to the placenta. Some other observations on foetal growth in mice are cited which are also consistent with the haemodynamic theory.

6-Aminopenicillanic acid VI. Formation of 6-aminopenicillanic acid from penicillin by enzymic hydrolysis

Abstract: Penicillin amidase activity, resulting in the hydrolysis of phenoxymethylpenicillin to give 6-aminopenicillanic acid, was found to be widespread among micro-organisms. Partial purification of the enzyme, which was essentially exocellular, was obtained by precipitation with ammonium sulphate, or acetone, followed by dialysis. The pH optimum with phenoxymethylpenicillin as substrate was found to be approximately 9$\cdot $0 with maximum enzyme stability at approximately pH 10$\cdot $0. Over a relatively short period of reaction time the optimum temperature was approximately 50 degrees C. The K$_{m}$ value with phenoxymethylpenicillin was found to be 4$\cdot $0 mg/ml. Using as substrate a concentration of 1% phenoxymethylpenicillin, a conversion to 6-aminopenicillanic acid of 56% of theoretical was obtained in the enzyme reaction mixture. Isolation of pure 6-aminopenicillanic acid from this reaction mixture was obtained in 50% yield. 6-aminopenicillanic acid markedly inhibited the enzyme activity at a concentration of 4$\cdot $0 mg/ml. Phenoxyacetic acid at this concentration was without effect. At higher concentrations, incubation of 6-aminopenicillanic acid and phenoxyacetic acid with the enzyme resulted in the synthesis of phenoxymethylpenicillin. The pH optimum for enzyme activity in the direction of synthesis was 5$\cdot $0 to 5$\cdot $5 compared with approximately 9$\cdot $0 for hydrolysis.

Visual pigments before and after extraction from visual cells.

Abstract: When retinal visual cells are suspended in equal-density sucrose solution, the resulting suspensions scatter light strongly. An opal-glass technique has been adapted so that the light truly absorbed by such suspensions can be separately characterized from the light scattered by them. Using this technique the properties of visual pigments in their natural cell environments have been compared with the properties of the same pigments after they have been extracted into digitonin solution. Pigments from three species, Rana temporaria, Conger conger and Cyprinus carpio, have been studied. In all cases it has been found that there is no detectable change in the light-absorbing properties of the visual pigments when they are extracted from their natural environment into solution. The photoproducts formed when the visual pigments are bleached in situ are significantly different, however, from the photoproducts ordinarily found in extracts. This finding has important consequences for the interpretation of difference spectra obtained from visual-cell preparations-whether suspensions or intact retinae.

The Association between the Hermit Crab Dardanus arrosor (Herbst) and the Sea Anemone Calliactis parasitica (Couch)

Abstract: The association between Calliactis parasitica and the Mediterranean hermit crab, Dardanus arrosor, has been re-examined. It was confirmed that, unlike the Atlantic crab, Pagurus bernhardus, Dardanus arrosor can display an active behaviour pattern which assists the transfer of Calliactis to its shell. Extensive trials showed, however, a marked tendency for crabs to divide into two groups: 9performers9, which show this behaviour almost without fail; 9non-performers9, which almost never show this activity. Most of the 9performers9 were females and the 9non-performers9 males. Calliactis frequently transfers to Dardanus-occupied shells without the crab9s help. Actively 9performing9 Dardanus often fail to transfer Calliactis to their shells. Observations on these cases and experiments with inactivated shells show that for successful crab-aided transfers the co-operation of the anemone is necessary. This co-operation depends on a response of the tentacles to the shell. Apparently it is similar to the 9clinging9 response to Buccinum shells at Plymouth, now known to depend on a molluscan shell-factor. Crabs and anemones from the Atlantic and the Mediterranean are able to form associations and display their normal behaviour patterns in response to individual partners from the other population. The results are discussed in relation to the possible origins and advantages of the association to the two partners in the two cases.

The Ferrier Lecture: The nature of central inhibition

Abstract: I feel greatly honoured by the invitation to give the Ferrier Lecture. I attended the first Ferrier Lecture, given by Sherrington in 1929, and I learned from Sherrington to value and admire the pioneer contributions of David Ferrier to neurology. In choosing the subject of inhibition for my lecture I was prompted by the peculiar challenge that inhibition has presented to physiologists ever since it was first demonstrated by the Weber brothers in 1846 that stimulation of the vagus nerve could stop the heart and by Setchenov in 1863 that stimulation of areas in the brain could slow or prevent reflex responses of frog limbs. It was Sherrington who greatly extended and organized knowledge of inhibition in the central nervous system; first, by a series of remarkable investigations, and finally by a theoretical paper published by the Royal Society in 1925, in which excitation and inhibition were given equivalent status in the synaptic mechanisms controlling neuronal discharge. His interest in central inhibition continued to the end of his scientific life, and was the subject of his Nobel Lecture in 1932. I might mention that both my first scientific paper and my D.Phil. thesis were concerned with inhibition, and that I have continued to be more interested in the problem of synaptic inhibition than in any other aspect of neurophysiology. In recent years progress has been so rapid that our understanding of the nature of central inhibition is in several respects more complete than that of central excitation. This illumination has followed rather rapidly upon a long period of ingenious theorizing which is now only of historical interest

Some Effects of Accelerating Growth. III. Behaviour and Nervous Activity

Abstract: The behaviour and nervous activity of rats which had been made to grow fast by a super-abundance of food in the first week or two of life were compared with the same characteristics in litter-mates which had been suckled in large litters, and gained weight much more slowly. The rapidly growing animals were more active and inquisitive at each chronological age than their slow-growing litter-mates, and they appeared to profit more by previous experience, which indicates that they learned more quickly. It is suggested that nutritional variables may underlie some of the correlations which have been found by others to exist between physical and mental development at similar chronological ages in children. It is also possible that children today, who are admittedly growing faster than they did 50 years ago, should be expected to display a correspondingly greater mental activity and ability to learn.

Arrest of Mitosis in Roots by Oxygen-Lack or Cyanide

Abstract: Excised pea-root tips were incubated in various conditions, in order to determine the effect upon mitosis In air the mitotic index rapidly decreased, but in an atmosphere of oxygen-free nitrogen (containing less than 0$\cdot $001% oxygen) mitotic figures persisted for up to 24 h Counts of the total number of cells showed that the persistence of mitotic figures represented an arrest of mitosis by anaerobiosis, and not a continuation of cell division as had previously been surmized The effects of oxygen-lack were simulated by 10$^{-2}$ M-sodium cyanide Mitotic arrest persisted for only about 4 h if industrial nitrogen (containing about 0$\cdot $05% oxygen) was used, or if 10$^{-3}$ M-cyanide was employed The cells thus partially arrested slowly continued the normal course of mitosis, and did not merely revert directly to interphase Similar results were obtained with different kinds of roots, and with intact seedlings The results were in accordance with an hypothesis that all stages of cell division depend upon the presence of oxygen, but that the visible stages of mitosis are less dependent than is the stage of entering mitosis

Pitch Discrimination in Locusts

Abstract: Sound stimulation of the tympanic organ of Locusta migratoria and Schistocerca gregaria initiates responses in the tympanic nerve and these in turn stimulate a few interneurones which ascend the ventral cord from the metathoracic ganglion to the brain. Some of the preparations show the following evidence of pitch discrimination. The response of the whole tympanic nerve to a pulsed note of low pitch cannot be made identical to the response to the same pulse at high pitch no matter how the relative intensities are adjusted. A continuous note, which presumably adapts some but not all of the primary receptors, modifies the relation between pre- and post-ganglionic responses in a way which depends on the pitch of the continuous note. The relative intensities of a pure tone of high pitch (10 to 15 kc/s) and one of low pitch (0$\cdot $5 to 2$\cdot $0 kc/s) can, in a preparation showing only 9on9 responses, be adjusted so that there is a post-ganglionic response to the former but not to the latter, although the latter causes a larger response in the tympanic nerve. Certain large interneurones, identifiable by their spike height, do not have the same curve of threshold to pulses of various pitch as does the summed response from the whole tympanic nerve. The post-ganglionic response is, therefore, towards a selected fraction of the sensory axons. In cach of the above tests the effects are small and pitch discrimination cannot be of great significance for the life of the animal.

Genetical Studies on the Skeleton of the Mouse. XXVIII. Tail-Short

Abstract: Mice heterozygous for the Ts gene have shorter tails and smaller bodies than their normal litter-mates. A study of their anatomy revealed skeletal abnormalities of various kinds scattered over the whole body. These abnormalities can be traced back to 11-day embryos, and are always accompanied by anaemia (which disappears before birth) and the consequent retardation. The anaemia in turn can be traced back still further to a deficiency of blood islands in the yolk sac of 8-day embryos. It is suggested that the primary effect of the gene is anaemia, which, acting through differential retardation of various organs, leads to the abnormalities seen later.

Dependence of mitosis and respiration in roots upon oxygen tension.

Abstract: Excised pea-root tips were incubated for 4 h in gas mixtures containing 0$\cdot $00001 to 100% oxygen, in order to determine the effect upon mitosis. Below 0$\cdot $0005% oxygen, mitosis was completely arrested. Between 0$\cdot $001 and 0$\cdot $2% oxygen, cells initially in mitosis completed division, but no more cells started dividing. Between 0$\cdot $05 and 0$\cdot $2% oxygen, cells initially in interphase entered division, but did not finish. Above 0$\cdot $5% oxygen, all cells not prevented from dividing by excision finished division within 4 h. After exposure to 0$\cdot $05% oxygen for 4 h, an excessive proportion of cells was found in prophase; in 0$\cdot $1% oxygen an excess of metaphases, and in 0$\cdot $2% oxygen an excess of telophases resulted. The oxygen uptake and carbon dioxide output of root tips were measured in a range of oxygen tensions and in anaerobic conditions. The relationship between oxygen uptake and oxygen tension was hyperbolic; a half maximum rate of oxygen uptake was obtained at about 10% oxygen. It was concluded that the respiration of root tips was limited by slow diffusion of oxygen through the tissue. From the carbon dioxide output it was estimated that the amount of energy available to isolated root tips under anaerobic conditions was about 1% of that available under aerobic conditions. Possible mechanisms whereby extreme oxygen-lack could arrest mitosis were considered. It was shown that the arrest was not due to abolition of a gross supply of energy. No evidence was obtained as to what other mechanism might be operative. An hypothesis was formulated in an attempt to explain the complicated relationship between mitosis and oxygen tension. It was assumed that the visible phases of mitosis are immediately preceded by a phase with a higher requirement for oxygen than mitosis, and that preceding this is an earlier phase with a lower oxygen requirement than mitosis.

Electrophoretic Characteristics of Ram and Rabbit Spermatozoa

Abstract: 1. The influence of a d.c. electric field on the direction in which ram and rabbit spermatozoa swim has been investigated. The magnitude of the electrophoretic component is so small in the presence of high salt concentrations ($\mu $ = 0$\cdot $1) that it plays no part in controlling the direction in which the spermatozoa swim. A significant electrophoretic velocity component can, however, be imposed if the spermatozoa are suspended in a diluent (277 mM-fructose) with a low ionic strength ($\mu $ < 0$\cdot $01). In this condition higher field strengths can be applied without any concomitant rise in temperature, and the $\zeta $-potential increases because the gegen-ion concentration is reduced. 2. In a diluent containing 277 mM-fructose and 10 mM-NaCl two types of spermatozoa are seen when the electric field is applied. Their orientation depends on whether they carry a net negative charge in the region of their heads or their tails. 'Head-anode' spermatozoa swim with unusual rapidity towards the anode but immediately decelerate when the field is switched off. 'Tail-anode' spermatozoa have a variable ground speed and may, if the field strength is high, be seen swimming tail first towards the anode. They accelerate away from the anode when the field is switched off. 3. The proportions of the two types of spermatozoa vary with salt concentration at constant pH, and with pH at constant salt (10 mM-NaCl) concentration. 4. If the swimming speed of spermatozoa is reduced by cooling, electrophoresis in the presence of high salt concentration ($\mu $ = 0$\cdot $1) differentiates spermatozoa into two kinds in another way. Both are oriented with their tails pointing towards the anode (tail-anode), but their net ground speed may vary in magnitude and direction according to their inherent swimming speed. Complete immobilization of the spermatozoa resulted in a uniform electrophoretic migration towards the anode, tail first, at all pH's above 3$\cdot $5. 5. The implications of these findings are discussed with respect to sperm phenotypes and their possible electrophoretic separation.

On the tropomyosin-paramyosin system in relation to the viscous tone of lamellibranch 'catch' muscle

Abstract: Some lamellibranch muscles are able to maintain tension for prolonged periods with very little energy expenditure, possibly by means of a special 9catch9 mechanism. Whilst actomyosin seems to be associated with active contraction, the 9catch9 might well be linked with tropomyosin A (TM$_{A}$) which is more abundant in these muscles than actomyosin (AM) and located in special filaments known as paramyosin. There is in fact a correlation of tropomyosin content and 9tonic9 properties in three different portions of Pecten maximus adductor muscle, the striated adductor (AM/TM = 9:1), the translucent portion of the smooth adductor (AM/TM = 2:1), and the opaque portion of the latter (AM/TM = 1:2). A typical 9catch9 can be demonstrated in the glycerinated fibres of the tropomyosin-rich but not in the tropomyosin-poor type by measuring fibre rigidity in presence of adenosine triphosphate (ATP) and Mg ions. Quick release and stretch experiments have shown that, unlike active contraction, rigidity in presence of ATP is not dependent on a functional AM system, which can be inactivated with Salyrgan, denatured with ethanol or plasticized with pyrophosphate. Instead, a change in fibre rigidity is always found to be associated with a change in the colloidal state of TM$_{A}$ when the latter is selectively modified in situ, as, for example, by varying the pH between 6$\cdot $5 and 8 or the ratio of the Mg-ATP chelate to 9free9 ATP. The latter increases the solubility and the electrophoretic mobility of TM$_{A}$ and it plasticizes artificial tropomyosin threads or the tropomyosin system in situ. Its action is best explained in terms of a decrease in protein-protein interaction caused by an increase in net charge due to binding, an effect which it counteracted by divalent cations which combine with ATP. Extrapolating these findings to the behaviour of living muscle one might tentatively suggest that the high rigidity of glycerinated tonic adductor muscle fibres in presence of Mg-ATP corresponds to the high muscle 9viscosity9 of tonically contracted living molluscan muscle and that free ATP acts as a physiological plasticizer, inducing changes in muscle 9viscosity9 by affecting the electrostatic tropomyosin-tropomyosin interaction either within or between the paramyosin (tropomyosin) filaments.