bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gas Exchange With Air and Water in an Air-Breathing Catfish, Saccobranchus (≡Heteropneustes) Fossilis
Authors: Hughes G. M. , Singh B. N. 
Published: April 2021

ABSTRACT
Gas exchange of Saccobranchus fossilis with water and air has been studied under various experimental conditions which were designed to simulate some of the conditions of tropical Asia. In tap water the fish exchanges gases with both water and air. When kept in air-saturated water it can exchange gases with water alone for periods of 6–12 h or even more. In de-oxygenated water, with free access to air, it obtains oxygen from the air and can five for several days under these conditions. In air-saturated water more oxygen is obtained from water (60 %) than from air (40 %), but in hypoxic water this ratio is reversed. When the fish is submerged in water, free access to air being prevented, the oxygen consumption is reduced, even in air-saturated water. In hypoxic and hypercarbic water oxygen consumption is further reduced. In air-saturated water about 17% of the oxygen enters via the skin and the rest via the gills. When exchanging gases with water alone and subjected to a gradual hypoxia, the fish shows a less dependent respirator. When the fish is removed from the water its oxygen consumption is reduced. A greater reduction occurs when the fish is kept in de-oxygenated water but allowed to breathe air. When the fish is exchanging gases with both water and air very little carbon dioxide is released into the air (RQ = 0·17). The total RQ in fish removed from the water is low, i.e. 0·58. The fish can survive in hypercarbic water only, provided that the content of carbon dioxide does not exceed 14·5 volumes %, when surfacing becomes necessary.
Connective Tissue Mechanics ofMetridium Senile: II. Visco-Elastic Properties and Macromolecular Model
Authors: Gosline John M. 
Published: April 2021

ABSTRACTThe visco-elastic properties of the body-wall connective tissue (mesogloea) of the sea anemone Metridium senile were previously studied by Alexander (1962). He carried out creep tests (extension under constant stress) over long periods of time and observed that the tissue could be extended reversibly to over three times its initial length with very small forces. The material behaved very nearly like a single Voigt element with a retardation time of about 3500 sec. Although Alexander did not propose any specific molecular mechanism to account for the extensibility and apparent slow elasticity, he did note that collagen is thought to be a major component of mesogloea and suggested that the collagen must play a major role in determining the mechanical properties of the tissue.
Coxal Muscle Receptors in the Crab: the Receptor Potentials of S and T Fibres in Response to Ramp Stretches
Authors: Bush B. M. H. , Roberts Alan 
Published: April 2021

ABSTRACT
Intracellular and extracellular recordings from the two large-diameter S and T sensory fibres of the posterior thoracico-coxal muscle receptor in shore crabs confirm the graded, dynamic-static nature of the receptor potentials evoked by stretching the receptor muscle, and the lack of afferent impulses. Slow ramp-function stretches evoke receptor potentials with characteristic shapes, which differ between the two fibres in several respects: The dynamic component in the S fibre resembles an algebraic sum of length and velocity responses and a variable initial ‘acceleration’ (?) transient, while in the T fibre it commonly declines (‘adapts’) during stretching, especially at greater velocities and starting lengths. On release of stretch the S fibre usually exhibits a ‘negative velocity response’, but the T fibre repolarizes rapidly often with a slight hyperpolarization. The dynamic response of the T fibre is generally greater than that of the S fibre, and increases more steeply and approximately logarithmically with stretch velocity over a 10- to 50-fold range. The’ static response ‘or degree of depolarization increases fairly linearly with receptor length in the S fibre but very non-linearly in the T fibre. The T fibre displays pronounced hysteresis in its dynamic and static responses at increasing and decreasing lengths, but the S fibre shows little hysteresis. The T fibre but not the S fibre commonly shows small rapid oscillations or ‘noise’ superimposed upon strongly depolarized ‘static’ potentials. The S and T responses may be affected reciprocally by some forms of receptor muscle contraction. Graded receptor potentials evoked in the ‘D’ fibre by stretching the non-muscular depressor-receptor strand of the coxo-basal joint show little hysteresis. Receptor muscle fibres respond to motor nerve stimulation or spontaneous motor impulses from the thoracic ganglion with slow, facilitating and summating excitatory junctional potentials. The mechanisms underlying the differences between S and T responses, and their functional significance to the animal, are discussed, and comparisons are drawn with other muscle receptors.
Experiments with the Isolated Heart of the Gastropod Helix Pomatia in an Artificial Pericardium
Authors: Civil G. W. , Thompson T. E. 
Published: April 2021

ABSTRACT
Isolated hearts of Helix pomatia could be maintained for 3–4 days at 19 °C in physiological saline. Co-ordination was soon lost, but irregular twitches could be observed for up to 115 h. A perfusion apparatus was designed which supplied a simulated venous return pressure of 8 cm saline and enabled in vitro survival of pericardium-free hearts for up to 2 days at 15 °C. Cessation of perfusion led immediately to a reversible stoppage of heart-beat. An artificial pericardium apparatus (APA) allowed the role of the pericardium to be studied. In the APA measurable translocation of fluid was effected by the heart, even when the simulated venous return pressure was negative. If the APA was transformed into an open system by opening up a simulated reno-pericardial canal, the effectiveness of the heart was greatly reduced. In the APA the greater the dilation of the heart (in consequence of decreased volume of pericardial fluid) the greater was the stroke volume for a given simulated venous return pressure. Results obtained with the APA give support to the theory that in the gastropod heart the filling of the auricle is hydrodynamically coupled (through the pericardial fluid) to the emptying of the ventricle.
Factors Affecting Blood Flow to the Lungs in the Amphibian, Xenopus Laevis
Authors: Emilio M. G. , Shelton G. 
Published: April 2021

ABSTRACT
A series of breathing movements which are effective in ventilating the lungs are accompanied by a marked increase in pulmonary blood flow and a decrease in pulmo-cutaneous arterial pressure. This reaction must involve considerable vasodilation of the pulmonary vascular bed. Similar vasodilation is produced by artificial inflation of the lungs via an implanted cannula. Nitrogen is not so effective as air in producing the vasodilation, whereas oxygen is more effective. It is suggested that both stretch receptors in the lungs and chemical receptors in lungs or blood are involved in the reaction. The level of anaesthesia is important in determining the degree of vasodilation response to the different stimuli. It is concluded that the central nervous system is the site where interaction occurs between signals from stretch receptors and chemical receptors and from the breathing movements themselves. Experiments with atropine suggest that the efferent pathway is in the vagus nerve. Recordings from free-swimming, unanaesthetized toads show that the vasodilation response occurs as part of normal diving-emergence behaviour.
Energetics of Hovering Flight in Hummingbirds and in Drosophila
Authors: Weis-Fogh Torkel 
Published: April 2021

ABSTRACT
Expressions have been derived for an estimate of the average coefficient of lift, for the variation in bending moment or torque caused by wind forces and by inertia forces, and for the power output during hovering flight on one spot when the wings move according to a horizontal figure-of-eight. In both hummingbirds and Drosophila the flight is consistent with steady-state aerodynamics, the average lift coefficient being 1·8 in the hummingbird and o-8 in Drosophila. The aerodynamic or hydraulic efficiency is 0·5 in the hummingbird and 0·3 in Drosophila, and in both types the aerodynamic power output is 22–24 cal/g body weight/h. The total mechanical power output is 39 cal g−1 h−1 in the hummingbird because of the extra energy needed to accelerate the wing-mass. It is 24 cal g−1 h−1 in Drosophila in which the inertia term is negligible because the wing-stroke frequency is reduced to the lowest possible value for sustained flight. In both animals the mechanical efficiency of the flight muscles is 0·2. It is argued that the tilt of the stroke plane relative to the horizontal is an adaptation to the geometrically unfavourable induced wind and to the relatively large lift/drag ratio seen in many insects. The vertical movements at the extreme ends may serve to reduce the interaction between the shed ‘stopping’ vortex and the new bound vortex of opposite sense which has to be built up during the early part of the return stroke. Two additional non-steady flow situations may exist at either end of the stroke, delayed stall and delayed build-up of circulation (Wagner effect), but since they have opposite effects it is probable that the resultant force is of about the same magnitude as that estimated for a steady-state situation. Most insects have an effective elastic system to counteract the adverse effect of wing-inertia, but small fast-moving vertebrates have not. It is argued that the only material available for this purpose in this group is elastin and that it is unsuited at the rates of deformation required because recent measurements have shown that the damping is relatively high, probably due to molecular factors.
Electrophysiological Studies on the Heart of the Bivalve Mollusc,Modiolus Demissus
Authors: Wilkens Lon A. 
Published: April 2021

ABSTRACTThe membrane potential in the heart of Modiolus demissus is dependent primarily on the unequal distribution of potassium ions across the cell. The membrane potential is low, however, and the reduced slope of the potassium equilibrium potential is not predictable by the familiar Nemst equation. The membrane undergoes a sustained depolarization in Cl-free SW which reduces the magnitude of subsequent potassium depolarization. Chloride ions contribute, perhaps independently, up to 15–30% of the total potential. The high degree of variability in membrane potential is due, in part, to a sodium leakage current. Membrane hyperpolarization in Na-free SW is greatest in hearts with a low initial potential. An electrogenic sodium pump is described which contributes to the membrane potential in the form of a rhythmical after-hyperpolarization (positive after-potential) following each spike. Inhibition of the pump (reduction of the after-potential) can be achieved using ouabain and cyanide, by substituting lithium for sodium, by removing extracellular potassium and by cooling the heart. The ionic basis of the membrane potential is discussed in relation to the diffuse pacemaker properties of the heart.
The Mode of Action Of 5-Hydroxytryptamine
Authors: Berridge M. J. 
Published: April 2021

ABSTRACT
The isolated salivary gland of the blowfly Calliphora has been used to study the molecular pharmacology of 5-hydroxytryptamine (5-HT). Ethylamine alone is inactive but the addition of extra carbon atoms or ring systems (imidazole or benzene) introduces some activity. A 5-hydroxyindole ring confers most activity. If the hydroxyl group is either removed, replaced with other groups, or displaced to the 4- or 6-position on the indole ring there is a large reduction in activity. The activity of the molecule is greatly reduced if the length of the side chain is decreased (gramine) or increased (3-aminopropyl indole) by a single carbon atom. Such molecules are effective competitors. These structure-activity studies suggest that the specificity of 5-HT resides in the 5-hydroxyindole moiety which binds the molecule to the receptor while the positively charged ethylamine side chain is responsible for inducing the hormonal effect.
The Effects of 5-Hydroxytryptamine and Cyclic Amp on the Potential Profile across Isolated Salivary Glands
Authors: Prince William T. , Berridge Michael J. 
Published: April 2021

ABSTRACT
The sites of the transepithelial potential changes produced by 5-HT and cyclic AMP in the salivary gland of the blowfly (Calliphora) have been investigated. Microelectrodes recorded a two-step potential profile across this epithelium. The cell was negative to both the bathing medium and the saliva. The basal membrane potential was 44·0 ± 0·2 mV and was affected very little by application of either 5-HT or cyclic AMP. The apical membrane was depolarized by 5-HT and in contrast was hyperpolarized by cyclic AMP. On the basis of these results it is concluded that 5-HT has two actions: (a) to stimulate a potassium pump on the apical membrane using cyclic AMP as an intermediary, (b) to increase chloride movement by a mechanism not directly involving cyclic AMP.
Aspects of Branchial Irrigation in the Lobster Homarus Americanus
Authors: Wilkens J. L. , McMahon B. R. 
Published: April 2021

ABSTRACT
The movements of the scaphognathites of the lobster, Homaros americanos, and the resulting thrust, were resolved in two dimensions accompanied by attack angle changes. Correlation of these scaphognathite and related body movements with branchial hydrostatic pressures during forward and reversed pumping were effected by simultaneously recording on video tape. Forward pumping maintains a negative pressure within the branchial chambers of 2·5–10 mm H2O superimposed on a maintained negative pressure relative to the outside of 0·5 mm H2O. The scaphognathite, by assuming a negative attack angle to the water during the upstroke of the beat, produces the positive pressure of reversals. Contraction of the epimeral attractor muscle appears to contribute to the re-establishment of branchial negativity following each reversal. This muscle inserts on the epimera and by contraction enlarges the branchial chamber. The role of reversals is discussed and it is concluded that their primary function is to clean foreign material from the border of hairs which filter incurrent water. Reversed beating may be a general response to all unusual stimuli to the respiratory system. The pattern of water flow into and through the gill chambers was determined. The relative volume of water entering each incurrent aperture between the legs was calculated and indicated that approximately equal volumes of water entered each aperture. It is concluded that forward pumping adequately irrigates all gill surfaces.
Temperature-Dependence of Permeability to Water and To Sodium of the Gill Epithelium of the Eel Anguilla Anguilla
Authors: Motais R. , Isaia J. 
Published: April 2021

ABSTRACT
The temperature dependence of diffusional permeability to water was studied in freshwater-adapted and seawater-adapted eels. The pattern of temperature acclimation is discussed. The ratio of water permeability to sodium permeability is approximately 3 at 25 °C, but falls to 1 at 5 °C. This drop is mainly due to a diminution of the water permeability, the temperature coefficients being much higher for water than for sodium. The relatively independent variations of water and sodium permeabilities in the seawater-adapted fish probably indicate a certain dissociation between water movements and salt movements. In the freshwater-adapted eel the osmotic permeability is considerably higher than the diffusional permeability, which supports the previously advanced hypothesis concerning the presence of water-filled channels in the branchial epithelium. In the seawater-adapted eel the osmotic permeability is lower than the diffusional permeability, this difference being greater the lower the temperature. This surprising result must signify either that the osmotic pressure difference between blood and sea water does not represent the true osmotic gradient across the membrane, or that a reabsorption of water linked with a movement of solutes occurs in a specialized region of the gill.
A System of Electrically Coupled Small Cells in the Buccal Ganglia of the Pond Snail Planorbis Corneus
Authors: Berry Michael S. 
Published: April 2021

ABSTRACT
The buccal ganglia of Planorbis contain a population of electrically coupled small cells. This has been studied, in preparations of isolated ganglia, by recording intracellularly from the cells two at a time. The population is usually silent but activity initiated in any one of its members tends to spread to the rest of the population in both ganglia. Failure of spread, or fatigue, gradually occurs on repetition. The group has the properties of a trigger system, initiating prolonged patterned activity in large numbers of neurones in the buccal ganglia. This may normally initiate feeding. In addition to central processes, both in the buccal ganglia and to the rest of the CNS, the system has peripheral axons in most of the buccal nerves. No synaptic input could be demonstrated. Action potentials in some of the cells increase greatly in duration with repetition. The resulting electrotonic EPSP’s, recorded in closely coupled trigger cells, correspondingly increase in size. The possible integrative significance of this is discussed, especially its effect in offsetting fatigue. In some preparations spontaneous bursting occurred in trigger cells and this elicited burst activity in large neurones, including motoneurones. The system may have an intrinsic pacemaker.
Cardiovascular and Respiratory Responses of Ducks to Progressive Hypocapnic Hypoxia
Authors: Jones David R. , Holeton George F. 
Published: April 2021

ABSTRACT
Cardiac ouput, ventilatory minute volume and gaseous exchange at both tissues and lungs have been recorded in restrained unanaesthetized ducks exposed to simulated high altitudes. A comparison between two species of duck showed that despite a significantly lower heart rate in resting Muscovy ducks, cardiac output, on a weight basis, was the same as in White Pekin ducks. Respiratory frequency and tidal volumes differed in the two species although their minute volumes were in the same range. Ducks responded to reduction in oxygen tension of arterial blood by increases in cardiac output and ventilatory minute volume, both being significantly above control (normal at rest) when was in the range 54·5–63 mmHg. At all levels of hypoxia ducks were able to remove about 30% of the oxygen from the ventilated air. When was 38 mmHg the difference between arterial and venous blood had decreased by 20·5 mmHg from control and during hypoxia and arterial and venous pH rose. The rate of oxygen uptake fell markedly at the lowest level of hypoxia but remained constant so that R.Q. rose from 0·76 at control at 1·12 at of 38 mmHg. It is concluded that there are many basic similarities between the cardiovascular and respiratory responses of ducks and mammals when exposed to simulated high altitude.
Plasma Chloride and Sodium, and Chloride Space in the European Eel, Anguilla Anguilla L
Authors: Kirsch R. 
Published: April 2021

ABSTRACT
New intra-vascular cannulation techniques are described, and also an extracorporal blood circuit containing an artificial heart and a counting cell. This makes possible a continuous study of the radioactivity of the blood. Plasma chloride concentration varies greatly in fresh-water eels despite good sodium regulation. The fresh-water to sea-water adaptation of eels is frequently accompanied by a temporary hypermineralization of the internal medium. This necessitates a high degree of cellular euryhalinity. The sea-water-adapted eel maintains strict homeostasis of its plasma chloride and sodium. The chloride distribution space decreases by 10% when eels are transferred from fresh water to sea water. The internal distribution of chloride is also modified and its fluxes between the ion compartments of the body are considerably increased.
Electrophysiological Analysis of Peripheral Neurones and Their Possible Role in the Local Reflexes of A Mollusc
Authors: Prior David J. 
Published: April 2021

ABSTRACT
It has been shown by behavioural and electromyographic studies that local reflexes exist in the siphon wall musculature of Spisula. In contrast, the responsiveness of the siphon retractor muscles is centrally mediated. Clusters of neurone somata occur at the peripheral branching points of the siphonal nerves. Intracellular records obtained from these peripheral cluster cells indicate they are efferents to the siphon wall musculature. These cells receive synaptic input from a population of touch-sensitive afferents from the siphons and mantle. None of the peripheral cells from which records have been obtained provided any indication of being sensory in function. ‘Central delay’ measurements indicate the presence of only one synaptic transfer between the afferent input to a peripheral nerve junction and the output of cluster cells. The synaptic input to the cluster cells is shown to be subject to short-term modification (antifacilitation). This coupled with the direct evidence that the peripheral cells are functional neurones supports the possibility that molluscan peripheral neurones could mediate habituated responses.
A Neural Correlate of Behavioural Stimulus Intensity Discrimination in A Mollusc
Authors: Prior David J. 
Published: April 2021

ABSTRACT
A behavioural sequence of Spisula is described that involves local reflexes, siphon retraction and valve adduction. The response to low-intensity tactile stimulation is locally mediated reflex activity of the siphon wall musculature. In response to medium-intensity stimulation, the siphon retractor muscles are activated along with local reflex activity. A neural correlate of this behavioural discrimination between low and medium stimulus intensities was obtained by simultaneous intracellular recordings from pairs of efferent neurones, one neurone type involved in local reflexes and one efferent tai the siphon retractor muscles. The peripherally located neurones of the siphon wall musculature (cluster cells) were found to have a lower spike threshold than the efferents to the siphon retractor muscles (pallial neurones). Several lines of evidence are presented that support the assumption that intra-somatic recordings from these neurones accurately reflect the activity of the synaptic region. The membrane electrical properties (i.e. input resistance, rheobasic current, threshold potential) of the two cell types were measured by passing current through single intrasomatic micro-electrodes. From these measurements it was found that the ‘critical firing level ’ of the cluster cells is significantly lower than that of the pallial neurones. By way of their differential sensitivities to synaptic input, the stimulusintensity discrimination could be mediated by cluster cells and pallial neurones directly.