bluuebunny/crossref_metadata_2025_split huggingface dataset:
Digestion in Ascidians and the Influence of Temperature
Authors: Berrill N. J. 
Published: April 2021

ABSTRACT
The mechanism of feeding and digestion in the Pyurid Ascidians Tethyum pyriforme americanum and Boltenia ovifera is described. The structure and histology of the “liver “is described and it is shown that it is primarily an organ of secretion. It is found that the only digestive enzymes are those poured into the gut by the liver, and consist of a powerful amylase, a protease, a very weak lipase, and also an invertase, a maltase, and a lactase. The brownish pigment of the liver gives reactions with acids somewhat like those of bile pigment. There is no trace of bile salts, however, nor of cholesterol. The amylase has an activity range from pH 6.0 to pH 8.5 with an optimum near pH 7·5. The protease is active from pH 6·0 to above pH 10·0. A similar protease is secreted by Molgula citrina and Ascidia prunum. The relative strengths of the amylase and protease are compared, the amylase being very much the stronger. While experiments of brief duration indicate an optimum temperature for enzyme activity above 40° C., the more prolonged the experiments the lower does the optimum become. Whatever the optimum may be after an experiment of 2 hours’ duration, it falls about 20° C. during the next 45 hours, if the experiments be so prolonged. At 15° C. and at 10° C. the food takes about 35 and 55 hours respectively to pass through the alimentary canal, and at 5° C. somewhere between 70 and 90 hours. These temperatures approximately cover the normal range in temperature of the environment, and therefore of the animal itself. From experiments lasting 33 hours the optimum temperature for enzyme activity was found to be about 17° C. ; that is, within one or two degrees of the body temperature. From experiments lasting 57 hours the optimum temperature was found to be about 13° C.; that is, within three degrees of the body temperature. These temperature optima not only represent the relative amounts of substrate converted at different temperatures, but also represent the absolute amounts converted and convertible. The enzymes, amylase and protease, are two-thirds to three-quarters destroyed during their period of activity within the alimentary canal of the animal, and in order to utilise the remainder the digestion mixture would have to be retained within the canal for twice as long a time. Therefore it seems probable that the organism in making such a compromise between a high activity of the enzyme and its economical use is working to a maximum efficiency ; and it is possible that a permanent increase in the stability of the digestive enzymes would be turned to advantage through a more prolonged retention of the food within the gut.
On the Spherical Form of the Mammalian Erythrocyte
Authors: Ponder Eric 
Published: April 2021

ABSTRACT
In 1895 Hamburger described a remarkable phenomenon which can be observed in suspensions of mammalian red cells in isotonic, hypotonic, or hypertonic saline and in sugar solutions, but not in serum or plasma. The normally biconcave discoidal cells become perfect spheres, without undergoing any apparent alteration in volume; the addition of serum to the suspension of spherical cells, however, converts the spheres back again into the typical discoidal form. Hamburger has no explanation to offer for the occurrence of this phenomenon, but suggests that it may be due to changes in surface tension.
In 1920 Brinkman and van Dam published a study of the phenomenon, in which they record the changes undergone by the red cells of man and of the rabbit when placed in a haemocytometer chamber. They correct Hamburger’s statement in one important respect, for they observe that red cells in saline are not spherical but discoidal, and that they become spherical only when placed in the haemocyto-meter chamber. In becoming spheres they pass through an intermediate form, “the crab-apple form,” which is spherical but finely crenated. Brinkman and van Dam believe that the cause of the phenomenon is that the cells receive an electrostatic charge from the glass when they come into contact with the floor of the chamber. They confirm Hamburger’s statement that the change from disc to sphere is prevented by the presence of serum, and claim that it is the cholesterol contained in the serum which inhibits the change of form.
Unaware of these two investigations, Gough in 1924 described the same phenomenon once gain, but fell into Hamburger’s error of believing that the red cells are spherical when suspended in a volume of saline. This error is very easy to make, and both Millar and I have made it also; indeed, as will be seen below, it is impossible to avoid it if an oil immersion objective is used for examining the cells. Gough adds two interesting observations to the previous descriptions: that ammonium oxalate and ammonium chloride act like serum in preventing the cells from becoming spherical in saline, and that the spherical form becomes crenated after a few hours, passing spontaneously into the discoidal form in about 24 hours. He does not give any detailed explanation of the phenomenon.
Both Millar and myself (Millar 1925, Ponder 1925) made the same mistake as Gough and Hamburger, in believing that the spherical form is due to the immersion of the cells in saline and that cells are spherical when freely suspended in this medium. On such an assumption, I carried out many measurements of sedimentation velocity without receiving any indication that the assumption was wrong1. It appears, however, on a more detailed examination, that the essential condition under which the spherical form occurs has escaped all the observers who have worked on the subject, and that the phenomenon is much more complex than has hitherto been believed.
The Modification of the Cloaca and Teeth of the Adult Salamander, Desmognathus, by Testicular Transplants and by Castration
Authors: Noble G. K. , Pope S. H. 
Published: April 2021

ABSTRACT
In 1926 de Beaumont showed that some of the secondary sexual characters of the male newt, Triturus cristatus, could be produced in the spayed female by testicular transplants. About the same time one of us (Noble, 1926) noted that cloacal glands could be made to arise de novo in the glandless cloaca of the female Desmognathus fuscus fuscus by the same method. Ponse (1923) with young females, and Welti (1925) with adult females, had previously demonstrated that toads which had been experimentally masculinised would develop nuptial pads. The above investigations were of interest in that they demonstrated, in both Caudata and Salientia, that structures not visible even as rudiments in the female could be made to appear and develop under the influence of the male sex gland.
A Method of Estimating the Scatter of Red Cell Populations from Their Diffraction Patterns
Authors: Ponder Eric 
Published: April 2021

ABSTRACT
All the existing methods for determining the diameter of red cells by the observation of the diffraction patterns which they produce are concerned with the determination of mean diameter only, and rest upon expressions which relate the position of the various maxima and minima to the diameter of a number of circular disks of uniform size (Pijper, 1919, 1923, 1925; Millar, 1926; Allen and Ponder, 1928). As is well known, the red cells which produce the diffraction patterns are not of uniform diameter, but it is assumed in the use of these methods that the diameter given by the formulae is the mean diameter of the red cell population.
The Water Balance of A Serpulid Polychaete, Mercierella Enigmatica (Fauvel)
Authors: Skaer Helen Le B. 
Published: April 2021

ABSTRACT
The accessibility of the coelomic and extracellular fluid compartments to the blood and the external bathing medium have been studied in the serpulid polychaete Mercierella enigmatica. Only the single cell layer of the blood-vessel walls separates the blood from the other body fluids. It is likely that this layer is relatively permeable to water and to molecules of low molecular weight so that changes in ion concentration at the surface of tissues, such as the muscles, probably parallel the extensive changes in the blood. Two types of longitudinal muscle fibre, differing in filament diameter, cell shape and distribution have been observed. The pattern of electrical activity recorded by intracellular micro-electrodes falls into two classes, separable on the basis of several parameters. This pattern is discussed in relation to the two types of longitudinal muscle fibre found.
Micromanipulation of the Flagellum of Crithidia Oncopelti
Authors: Holwill M. E. J. , McGregor J. L. 
Published: April 2021

ABSTRACT
The behaviour of the flagellum of Crithidia oncopelti when subjected to constriction and dissection by a microprobe was investigated. Constriction of the flagellar tip resulted in wave reversal, whereas dissection of this region allowed normal wave movement. Constriction of the basal region allowed both base-to-tip and tip-to-base propagation. The observed behaviour is more easily explained in terms of a sliding filament model of flagellar movement than by a model which involves local contraction.
Neuromuscular Physiology of the Longitudinal Muscle of the Earthworm, Lumbricus Terrestris
Authors: Drewes C. D. , Pax R. A. 
Published: April 2021

ABSTRACT
Patterns of innervation of the longitudinal muscle of the earthworm, Lumbricus terrestris, were examined electrophysiologically. The longitudinal musculature of a segment is innervated by relatively few axons, a fast and slow axon being present in segmental nerve I and in the double nerve, segmental nerve II–III. Single-pulse stimulation of the fast axon produces large external muscle potentials and small twitch-like contractions, which with repetitive stimulation are antifacilitating. Repetitive stimulation of the slow axon produces large, slowly developing and sustained mechanical responses, with electrical and mechanical responses showing summation and facilitation. The amplitude and time course of slow mechanical responses are related to the frequency of stimulation. Individual longitudinal muscle fibres are innervated by either the fast or slow axon in a segmental nerve, or by both fast and slow axons. No evidence was found for peripheral inhibitory innervation of the longitudinal muscle.
Neuromuscular Physiology of the Longitudinal Muscle of the Earthworm, Lumbricus Terrestris
Authors: Drewes C. D. , Pax R. A. 
Published: April 2021

ABSTRACT
The motor fields of individual segmental nerves have been mapped electro-physiologically in the longitudinal muscle of the earthworm, Lumbricus terrestris. The anterior pair of segmental nerves (SN I) innervates approximately the anterior two-thirds of its segment and a small portion of the segment just anterior to it. The posterior pair of segmental nerves (SNII-III) innervates approximately the posterior two-thirds of its segment and a small portion of the segment just posterior to it. Adjacent nerves (both intrasegmental and intersegmental) have partially overlapping motor fields; that is, adjacent segmental nerves innervate some of the same longitudinal muscle fibres.
Electrical Potential Differences and Ionic Transport in the Larva of the Mosquito Aedes Aegypti (L.)
Authors: Stobbart R. H. 
Published: April 2021

ABSTRACT
Measurements have been made, in the 4th-instar freshwater larva of the mosquito Aëdes aegypti, of (i) potential differences between haemolymph and medium; (ii) the effects upon sodium fluxes of metabolic inhibitors and of sodium-free solutions. The measurements of potential differences together with those of the Na, Cl, and K concentrations in the larvae show that Na and Cl are actively transported from the medium into the haemolymph, whereas K is probably taken up passively in company with Cl. Using Goldman’s constant-field equation and the present, and earlier, data it can be shown that the expected passive fluxes of Na and Cl between the larvae and the medium are very much smaller than the observed fluxes. KCN and de-ionized water immediately reduced Na outflux to one-sixth to one-seventh of the normal value; KCN also inhibits Na influx more or less completely. The passive Na fluxes through the anal papillae (which cause almost all the ionic movements) appear to be very small. Overall the data show that the influxes and outfluxes of Na and Cl cannot be explained in terms of passive movements. Nor can the increased outflux of these ions which is observed at high external concentrations be explained by Kirschner’s theory of ‘back-transport’. The data, however, are fully compatible with a model for ionic pumps suggested earlier, which would cause both net uptake and exchange of an ion. The data are discussed in terms of a refined version of this model.
Pressure Distribution on the Body Surface of Swimming Fish
Authors: Dubois Arthur B. , Cavagna Giovanni A. , Fox Richard S. 
Published: April 2021

ABSTRACT
Although there are a number of papers on how fish swim (Gray, 1957; Aleev, 1969; Lighthill, 1969), we have been unable to find any measurements of the pressure on the body surface measured while a fish is swimming. A preliminary calculation using the Pitot equation indicated that the pressure against the anterior surface of the fish, expressed in centimetres of water, would be approximately equal to the square of the speed of the fish in miles per hour. A fish one foot long, swimming at six miles per hour, would have a pressure of about 36 cm H2O against the front of his head. Such pressures, if actually present, might be large enough to affect the body functions, particularly circulatory, and ultimately influence the body structure of aquatic animals. They are of the same order of magnitude as the hydrostatic pressures due to gravity acting on land animals of equal body size, and as the blood pressure in fish (Satchell, 1971). In addition, the determination of the pressure distribution on the body surface of swimming fish may be of help in explaining the mechanism of fish locomotion. Compared to pressure distribution on the body surface of dead fish, or casts, the difference may be responsible for the otherwise unexplained ability of some fish to sustain locomotion with relatively little energy expenditure (Gray, 1957; Schmidt-Nielsen, 1972). In this study we measured the pressure on the body surface of swimming bluefish, and we speculate as to the physiological implications of the pressures which were found.
Oxygen—Sensitive Elements in the Book Gills of Limulus Polyphemus
Authors: Crabtree Robert L. , Page Charles H. 
Published: April 2021

ABSTRACT
The unit responses of oxygen-sensitive elements in the book-gill lamellae of Limulus polyphemus were examined by recording their unit activities in the gill nerve while varying the oxygen tension in the sea water bathing the lamellae. Three types of oxygen-sensitive units were detected. Some units (class I) were excited by oxygen introduced into anaerobic sea water; others (class II) were inhibited by high oxygen levels. Some units responded to tactile stimulation only in the presence of oxygen. It is suggested that the oxygen-dependent ventilatory reflexes result from interaction in the central ventilatory neural system of the excitatory effects of class I units and of touch-sensitive oxygen-dependent units with the inhibitory effects of class II units.
Studies on Locust Neuromuscular Physiology in Relation to Glutamic Acid
Authors: Clements A. N. , May Terry E. 
Published: April 2021

ABSTRACT
Two nerve-muscle preparations were used to investigate the physiology of the locust retractor unguis muscle in relation to L-glutamic acid. These were an ‘isolated preparation’, in which the muscle and its nerve were dissected out, and a ‘perfused-femur preparation’, in which the muscle suffered no mechanical disturbance. Exposure of the nerve-muscle preparations to glutamate caused a variety of responses, some of which were shown to be abnormal and due to the experimental conditions. When locust femora were perfused with saline or haemolymph the retractor unguis muscles were much more severely affected by glutamate if the hydrostatic pressure was slightly raised. At raised pressures the perfused-femur preparations were particularly prone to give repetitive and spontaneous contractions. Analysis of haemolymph from adult male locusts showed that it contained, on average, 0·2 mmol/1 L-glutamate, 45 mol/1 total non-peptide amino acids, 5·0 mmol/1 calcium, and 11·6 mmol/1 magnesium. It was calculated that approximately 50% of the calcium and 75% of the magnesium ions are bound to amino acids, and that approximately 25 % of the glutamic acid is bound to divalent metal ions. The isolated preparations were severely affected by glutamate at the concentration at which it occurs in haemolymph, and it was concluded that in the intact locust some mechanism must protect the neuromuscular synapses from haemolymph glutamate. No evidence could be obtained of the sequestration of glutamate by haemocytes, or of binding of glutamate to haemolymph proteins. Calcium and magnesium ions reduced the sensitivity of nerve-muscle preparations to glutamate to a greater extent than could be accounted for by the formation of amino acid-metal complexes. This suggests that the protection afforded by calcium and magnesium involves an interaction of the metal ions with the neuromuscular system itself. The retractor unguis muscle was much less sensitive to glutamate when it was contained within an undissected femur than in an isolated preparation. It was concluded that the muscle is normally protected from haemolymph glutamate by a diffusion barrier which is damaged on dissection. Comparison of the fine structure of retractor unguis muscles, fixed either after dissection or while still contained within the femur, showed that dissection normally caused a partial separation of muscle fibres and damage to the connective tissue sheath, with the resultant exposure of some nerve endings. The connective tissue sheath may constitute the postulated diffusion barrier. The excitatory synapses of the locust retractor unguis muscle are believed to be isolated from haemolymph glutamate by a diffusion barrier, which is tentatively identified with the connective tissue sheath that binds the muscle fibres together. Calcium and magnesium ions reduce the sensitivity of nerve-muscle preparations to glutamate, and may have such a role in the living insect.
Control of Head Movement in the Locust, Schistocerca Gregaria
Authors: Shepheard Peter 
Published: April 2021

ABSTRACT
Head movement in the locust Schistocerca gregaria is mediated by 14 pairs of muscles. The normal motor output to many of these muscles has been investigated in the intact insect by recording with two intracellular microelectrodes from different fibres of a muscle during slow and fast phases of optokinetic nystagmus elicited by rotation of a striped drum in the visual field. In addition, details of the innervation pattern and muscle fibre spectrum of the muscles have been investigated by paired intracellular recording during graded stimulation of the motor nerves in the dissected preparation. Of more than 60 different axons shown histologically to innervate the neck muscles on each side, the activity of about 25 have been analysed and deductions are made about the way the muscles work together in concert to produce head movement. At least four physiologically distinct types of axon innervate several muscles. These types are tonic (slow), phaso-tonic (intermediate), phasic (fast) and inhibitory. Stationary head positions are maintained by low levels of motor output in the tonic axons alone, these axons also being mainly responsible, when active at higher frequency, for producing small slow head movements. Phaso-tonic axons become progressively more active during larger or faster head movements to augment the effect of tonic axon activity. The fastest head movements are correlated especially with activity of the phasic axons. Inhibitory neurones are active during and immediately before rapid head movements, the output to individual muscles being correlated with both contraction and relaxation. On the basis of their electrical responsiveness to the axons innervating them, muscle fibres have been classified into the following types: ‘phasic’, ‘intermediate’ and ‘tonic’, with the tonic class subdivided into ‘ordinary tonic’, ‘super-tonic’ and ‘super-sensitive’. Some muscles contain only a small range of fibre types, while others contain the complete range. Deductions are made about the way the different axon types interact on the different muscle fibre types to elicit various degrees of contraction or tension. The slow phase motor output patterns are the result of a centrally determined programme elicited by visual input (rotation of the striped drum), and are not dependent on, but may perhaps be modified by, proprioceptive feedback. On the other hand, the fast phase of nystagmus is initiated by the central nervous system only after reference to the proprioceptive input from various sense organs of the neck and prothorax.
Net Fluxes of Water in the Isolated Gills of Anguilla Dieffenbachii
Authors: Shuttleworth T. J. , Freeman R. F. H. 
Published: April 2021

ABSTRACT
Measurements of net flux of water have been made on isolated gills removed from freshwater-adapted and seawater-adapted eels and incubated in various media of differing osmotic pressure. From these measurements it has been possible to determine the osmotic permeability coefficient of the gill directly from the net water flux. The values obtained (0 · 50 +0 · 14 × 10−5 cm.sec−1 for freshwater eels and 0 · 43 ± 0 · 07 × 10−6 cm.sec−1 for seawater-adapted eels) indicate that there was no significant change in this parameter on adaptation of the eels to sea water. The direct measurements made of the net water flux across the isolated gills appear to be compatible with the osmoregulatory pattern of eels as deduced by other workers using different techniques. In particular they illustrate and further emphasize the significance of drinking in the freshwater fish. Calculations indicate that, for a freshwater teleost, the osmotic and ionic problems caused by drinking in fresh water have an insignificant energetic effect and hence, energetically, it matters little to the fish whether it drinks or not.
Neuronal Modulation of Photoreceptor Activity in the Bee Moth Galleria Mellonella
Authors: Koopowitz Harold , Stone George 
Published: April 2021

ABSTRACT
Pairs of light stimuli given at varying intervals causes changes in fast-adaptation characteristics in the bee moth Galleria mellonella. With increasing intervals between the stimuli of up to 1·0 sec there is a decrease in the amplitude of the visual response to the second stimulus. This depression of the response can be affected by a variety of agents which alter synaptic activity. Application of compounds such as Mg2* and nicotinic acid, which block synapses, to the optic ganglion lift depression. K+ and CO2 applied to the optic ganglion also abolish adaptation. Severing neuronal connexions between the retina and ganglion also lifts the depression. De-ganglionation and nicotinic acid also result in increases in absolute amplitude of the response. If Ca2+ is added to the Ringer bathing the ganglion, adaptation becomes more marked. These results suggest that the decreases in sensitivity following a brief light stimulus are mediated by synaptic feedback onto the receptor cells.