bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies on Amphibian Metamorphosis
Authors: Helff O. M. 
Published: April 2021

ABSTRACT
The histolysis of the anuran operculum during forelimb perforation formation has been accredited to the action of autolysing gill tissue, to cutaneous gland secretions, and to self-degeneration of the integument by Helff, Weber, and Blacher et al. respectively. The writer has reinvestigated the problem as follows:
Opercular integument, homoplastically transplanted to the back and side of R. temporaria larvae, underwent a process of partial degeneration. The histolysis was not confined to any localized region of the transplant. Autoplastic transplantation of opercular integument to the back and side produced a variety of results. Normal histological structure was maintained in certain transplants, generalized degeneration was observed in others, while in several instances localized histolysis resulting in perforation formation occurred. Homoplastic and autoplastic transplantation of back and side skin to the opercular region resulted in histolysis and perforation formation in such transplants during larval involution. The right forelimbs (in early stages of development) with attached portions of the shoulder girdle were extirpated in R. temporaria and B. bufo. During subsequent metamorphosis, normal opercular histolysis followed by perforation formation in many cases was observed. In most instances, serial sections of the peribranchial cavity revealed the absence of cutaneous glands. Extirpation of the right forelimb only was made in the same two species. Opercular histolysis subsequently occurred in all instances, resulting in perforation formation in the great majority of cases during larval involution. In many of the B. bufo animals two separate perforations developed, one filled with limb stump and the other with gill tissue. It is concluded that in R. temporaria a particular area of the operculum may in some individuals possess self-degenerative potentialities conducive to histolysis and perforation formation during metamorphosis. In both R. temporaria and B. bufo histolytic influences emanating from the atrophying gill tissue and the cutaneous glands of the forelimb are probably also responsible for operêular histolysis and perforation formation. Limb pressure must be considered a supplemental factor. The results are discussed in general and attention called to the fact that opercular histolysis and perforation formation are “doubly assured” in some species and possibly even “triply assured” in others. Emphasis is placed on the evidently wide divergence between species as regards the particular combination of factors responsible for opercular histolysis and perforation formation. Apparently, no one explanation can serve to account for the phenomenon as it occurs in various species of anurans.
Potentials and Effective Ionic Mobilities in Frog Skin
Authors: Dean R. B. 
Published: April 2021

ABSTRACT
Frog skin has been used by many workers in the study of bioelectric phenomena of living membranes. The isolated living skin mounted with Ringer’s solution on both sides maintains a potential of from 10 to 100 mV., the inside of the skin being positive. This potential can be modified by changing the chemical or physical conditions. Many workers have attempted to interpret the results of such changes in terms of simple membrane potentials but without much success. Dean & Gatty (1937) point out some of the difficulties of such interpretation and review the literature. There is evidence of at least two sources of potential in the skin which may at times be opposed (Steinbach, 1933), and also that the active surfaces are not uniform but present a mosaic structure (see also Dean, 1938).
Experiments on the Effect of Dyes on Induction and Respiration in the Amphibian Gastrula
Authors: Beatty R. A. , de Jong S. , Zieliński M. A. 
Published: April 2021

ABSTRACT
It is shown that pieces of presumptive epidermis (ventral ectoderm of the gastrula), when isolated into weak solutions of several dyes, will undergo neural differentiation. Dyes such as Janus green and neutral red, which are not known to accelerate cell respiration, appear to have this effect, as well as methylene blue, the accelerating action of which on cell respiration is well known. Measurements of the oxygen consumption of isolated pieces of the gastrula by the Cartesian Diver method show that methylene blue, if in weak concentration, has an accelerating action of about 45 %. In stronger concentrations it is inhibitory.
The Micro-Estimation of Sodium, Potassium, Calcium, Magnesium, Chloride, and Sulphate in Sea Water and the Body Fluids of Marine Animals
Authors: Robertson J. D. , Webb D. A. 
Published: April 2021

ABSTRACT
Methods are presented for the estimation of sodium, potassium, calcium, magnesium, chloride and sulphate in sea water and in other solutions, such as the blood and body fluids of marine animals, whose inorganic composition is similar to that of sea water.
The estimations may be performed on 1 ml. samples, and the limit of error is about 2 %.
Sodium is precipitated and weighed as sodium zinc uranyl acetate ; potassium is precipitated as potassium silver cobaltinitrite which is titrated with ceric sulphate ; calcium is titrated with ceric sulphate after two precipitations as oxalate ; magnesium is precipitated with hydroxyquinoline and the precipitate brominated and estimated iodometrically; chloride is treated with silver iodate and the released iodate estimated iodometrically; sulphate is titrated with barium chloride using sodium rhodizonate as indicator.
On The Physiology and Pharmacology of the Earthworm Gut
Authors: Wu K. S. 
Published: April 2021

ABSTRACT
The physiology of the gut movements in invertebrates has been little studied. In the case of the earthworm, although numerous investigations have been published on the physiology of locomotion and of the neuro-muscular structures of the body wall, nothing has yet appeared on the gut movements. It was with the intention of throwing light on this problem that the present investigation was undertaken.
A Method for the Direct Study of Natural Selection
Authors: Gordon Cecil 
Published: April 2021

ABSTRACT
Decisive experiments on selection of mutants of Drosophila melanogaster can be carried out under natural conditions in Britain where this species is not indigenous. This communication records an experiment in which a balanced population containing 25 % ebony mutants was released in South Devon. The frequency of the genotype among the descendants was estimated after a period equivalent to six discrete generations, by testing trapped flies, most of which were wild type in appearance, for heterozygosis. The frequency estimated was very close to what would be deduced on the assumption that elimination of the recessive type before maturity was complete.
Central Nervous Activity in the Earthworm
Authors: Collier H. O. J. 
Published: April 2021

ABSTRACT
Regular rhythmic peristaltic movements of a preparation consisting of 20–40 complete segments of the earthworm may be initiated by longitudinal tension and by certain types of tactile stimulation. Peristaltic movements do not occur in such a preparation in the absence of stimulation, and cease within a finite period after the cessation of a stimulus. Peristaltic movements do not occur after excision of the nerve cord. The rhythmic responses to tension and touch are therefore together described as the peristaltic, reflexes, and the response to tension is individually described as the tension reflex. The preparation shows a variety of responses to touch. Tactile stimuli may evoke peristalsis; they may also elicit arhythmic contractions accompanied by immobilization of peristalsis. The peristaltic reflexes can be immobilized both by heavy vibration of the apparatus, and by certain tactile stimuli. The immobilization can occur without the accompaniment of any arhythmic contraction of the preparation. The immobilization can be referred to as an inhibitory process, since it exhibits features characteristic of inhibition: (i) lessening in the amplitude of beat in recovery from complete immobilization; (ii) reduction of the frequency of beat in the same circumstance. The inhibition of peristalsis is conducted through the central nervous system. The inhibitory effect persists for a considerable period after cessation of the stimulus. Inhibition may be followed by “rebound”. “Rebound” may be caused by the subsidiary exciting effect of the inhibitory stimulus.
Central Nervous Activity in the Earthworm
Authors: Collier H. O. J. 
Published: April 2021

ABSTRACTThe tension reflex in a number of isolated intact segments of the earthworm exhibits a definite threshold to weight. The value of the threshold in the series of preparations tested, varies between 0·1 and 1·0 g., measured as direct tension applied to the preparation. There is also a threshold for the duration of application of the weight. In the figure shown this lies above 0·5 sec. After an applied stimulus has been removed the peristaltic response of a preparation may continue for a finite length of time which seldom exceeds 3 min. The period for which the movement persists after the stimulus has been removed depends on the magnitude of the stimulus applied but not on the height of the contractions occurring. This fact is taken to support the view that the continuation of the response after the stimulus has been removed is a true after-discharge, due to a persistence of excitement in some region of the reflex arc. The after-discharge consists of a co-ordinated movement of both muscle sets which may be perfectly rhythmic. The after-discharge may be inhibited by suitable stimuli. The frequency of the after-discharge may be increased by the application of a stimulus of a different type from that which elicited the original response. When the preparation is submitted to a continuous tension, the response dies away within a period which does not normally exceed 25 min. The rate of beat in these circumstances shows three phases : a phase of acceleration, a plateau phase and a phase of decline. After the disappearance of a reflex under continuous stimulation, the response can be elicited once more by the addition of further tension. The frequency of beat in any one preparation shows a well-defined upper limit which, over the series of experiments carried out, was never observed to exceed 1 beat in 2·0 sec. The maximum frequency of beat is obtained with tensions intermediate between those of threshold value and those near the upper limit of endurance of the preparation. Lower and higher tensions than that producing maximum frequency produce submaximal rates of beat. The range of variation between rates of beat produced by a series of different tensions is less than the range of tensions used. After a tension reflex has been evoked, an increase in the weight applied may accelerate a submaximal frequency of beat, but cannot force the rhythm above its maximum. Large increments in weight lower the rate of beat. The rate of beat of a tension reflex may be accelerated by the application of a tactile stimulus and the frequency of a response to tactile stimulation may be accelerated by the application of tension. By whatever stimulus the acceleration of beat of a reflex is carried out, it is not accompanied by any break in the rhythm.
Regulation of the Haemolymph in the Saline Water Mosquito Larva Aedes Detritus Edw
Authors: Beadle L. C. 
Published: April 2021

ABSTRACT
The larvae of the mosquito Aedes detritus have been reported only from definitely saline waters. They have been found in water of salinity equivalent to c. 10 % NaCl. In the laboratory they were acclimatized with ease to distilled water, sea water (7 % NaCl), 3 ·5 % NaCl, and glycerol (3 ·5 % NaCl). They also show considerable resistance to N/20 NaOH, but less to N/20 KOH and N/50 HC1. They are unable to live permanently in solutions of the chlorides of potassium, calcium and magnesium of osmotic pressure equivalent to 3 ·5 % NaCl. In sea water of varying salinity they can regulate both the total osmotic pressure and chloride content of the haemolymph. A rise from nil to 6 ·0 % NaCl in the osmotic pressure of the medium is reflected in an increase of from c. 0 ·8 % to 1 ·4% NaCl in that of the haemolymph. In hypotonic solutions and distilled water much chloride is lost, but this is compensated by an increase in the non-chloride fraction. In hypertonic sea water the rise in osmotic pressure is due to increase in the chloride fraction, the nonchloride fraction remaining constant. From this and from experiments with non-electrolytes it is concluded that the larva is permeable to salts and to molecules as large as glycerol, and that the regulatory mechanism in hypertonic saline is concerned with compensation rather for penetration of salts than for loss of water by osmosis. Ligature experiments suggest that this mechanism is the excretion of salt by the Malpighian tubes, but further proof is required. Salt exchange with the environment takes place via the gut, the body surface being impermeable to salts and water. The larvae are able to concentrate chloride from hypotonic solutions but not as effectively as fresh-water species and only when the chloride content of the medium is a little below that of the haemolymph. The anal gills, as in all salt-water species, are very small and appear to be impermeable to salts and water. It is therefore concluded that they are not the seat of the chloride-absorbing mechanism. The osmotic pressure of the haemolymph is trebled by treatment with glycerol (3 ·5 % NaCl), which must be mainly the result of penetration of glycerol. The larva will however live normally in this, and an important factor in the resistance to abnormal media is therefore the adaptability of the tissues to changes in the concentration and composition of the haemolymph. The increase in the osmotic pressure of the haemolymph induced by hypertonic sea water and glycerol does not alter the amount of fluid in the tracheoles. This is discussed in relation to the possible mechanism for the absorption of the trecheóle fluid.
The Intact Central Nervous System of the Newborn Opossum in Long-Term Culture: Fine Structure and Gaba-Mediated Inhibition of Electrical Activity
Authors: Stewart R. R. , Zou D.-J. , Treherne J. M. , Møllgård K. , Saunders N. R. , Nicholls J. G. 
Published: April 2021

ABSTRACT
The entire central nervous system (CNS) of the newly born, South American opossum (Monodelphis domestica) was isolated and maintained in basal medium, Eagle’s (BME) with 0.2% foetal calf serum and antibiotics. Isolated CNS preparations remained electrically excitable for up to 10 days. The fine structure of the spinal cord was normal after 5 days in culture: axons, synapses, dendrites and glia were virtually unchanged. Signs of degeneration were evident only in dorsal areas of the spinal cord, which had been denervated by removal of the dorsal root ganglia during dissection. Amino acid transmitters such as glycine, glutamate, N-methyl-D-aspartate (NMDA) and gamma-aminobutyric acid (GABA), applied to the bathing fluid, rapidly and reversibly inhibited synaptic transmission in cervical segments of the spinal cord. GABA (10–100 μmoll−1) produced a dose-dependent reduction in the magnitude of ventral root responses evoked by dorsal root stimulation. GABA also inhibited synaptically activated compound action potentials produced by spinal cord stimulation. Dose-response curves for GABA obtained in different preparations were highly reproducible. Both GABAA and GABAB receptors were reversibly activated by selective agonists and inhibited by specific antagonists. The actions of GABA were potentiated by benzodiazepines, competitively antagonised by bicuculline (a selective GABAA antagonist) and mimicked by muscimol (a GABAA agonist). Baclofen (a specific GABAB agonist) also inhibited electrical activity and was competitively antagonised by the GABAB antagonist, CGP 35348. After 5 days of culture in BME or minimal essential medium (MEM), GABA dose-response curves were unchanged from those observed immediately after removal of the CNS. The inhibitory potency of baclofen was also unaffected by culture in BME. By contrast, after 5 days of culture in MEM, baclofen no longer inhibited electrical activity. This difference between BME and MEM could be attributed to the higher content of L-histidine in MEM. Thus, addition of 150 μmoll−1 L-histidine to BME produced similar results to culture in MEM: the inhibitory action of baclofen was virtually abolished after 3–5 days. L-Histidine had no effect on freshly dissected preparations. Chronic application of L-histidine did not affect glycine or glutamate responses after 5 days. Addition of D-histidine or other amino acids, such as arginine, to BME did not abolish the responses to baclofen. These results show that the isolated CNS of the newborn opossum survives well in long-term culture and that it provides a useful preparation to study receptor development and plasticity of an intact mammalian CNS in vitro. The rapid and reversible penetration of agonists and antagonists into the preparation also allows for pharmacological manipulation of the neuronal environment.
Addition of Artificial Loads to Long-Eared Bats Plecotus Auritus: Handicapping Flight Performance
Authors: Hughes Patsy M. , Rayner Jeremy M. V. 
Published: April 2021

ABSTRACT
A series of experiments is described in which two brown long-eared bats Plecotus auritus Linnaeus (Chiroptera: Vespertilionidae) were flown in a 1 m ×1 m×4.5 m flight enclosure at a range of body masses (n=9 experiments for a female bat, and n=11 for a male bat). The highest three of these masses incorporated artificial loads. Stroboscopic stereophotogrammetry was used to make three-dimensional reconstructions (n=124) of the bats’ flight paths. Over the entire range of experiments, wing loading was increased by 44% for the female and 46% for the male bat. Effects arising from captivity were controlled for: experiments at certain wing loadings were repeated after a period in captivity and the response to load was found to be unaltered. Flight speed fell with total mass M or with wing loading, varying as M−0.49 in the female and M−0.42 in the male bat. Wingbeat frequency increased with total mass or wing loading, varying as M0.61 in the female and M0.44 in the male bat. Hence frequency, but not speed, changed with mass in the direction predicted by aerodynamic theory. These results were used in a mathematical model to predict wingbeat amplitude, flight power and cost of transport. The model was also used to estimate the optimal flight speeds Vmr and Vmp. The model predicted that amplitude increases with load. Measurements of wingbeat amplitude did not differ significantly from the predicted values. The observed flight speed was below the predicted minimum power speed Vmp (which increases with load), and diverged further from this with progressive loading. The increase in cost of flight calculated by the model over the range of wing loadings was approximately double that which it would have been had the bats adopted the optimal approach predicted by the model. The limitations inherent in the theoretical model, and the possible constraints acting on the animals, are discussed.
Voltage-Activated Ionic Currents in Myoepithelial Cells Isolated from the Sea Anemone Calliactis Tricolor
Authors: Holman Molly A. , Anderson Peter A. V. 
Published: April 2021

ABSTRACT
Myoepithelial cells were isolated from the apical ends of mesenteries of the sea anemone Calliactis tricolor and examined using the whole-cell configuration of the patch-clamp technique. The isolation procedure produced cell fragments that were contractile and produced action potentials when depolarized. These action potentials are formed by a complex array of ionic currents consisting of at least one, and possibly two, inward calcium currents and four outward potassium currents. The ionic selectivity of the calcium currents was Ca2+&gt;Sr2+&gt;Ba2+. Outward currents consisted of a calcium-dependent outward current and three voltage-activated currents, including a 4-aminopyridine-sensitive current, a transient outward current and a steady-state current.
The Dopamine and 5-Hydroxytryptamine Content of Locust and Cockroach Salivary Neurones
Authors: Gifford A. N. , Nicholson R. A. , Pitman R. M. 
Published: April 2021

ABSTRACT
The salivary glands of the cockroach and locust are innervated primarily from two pairs of motoneurones, designated SN1 and SN2, in the suboesophageal ganglion. Intracellular cobalt fills and subsequent silver intensification were used to reveal the morphology of these cells in both species.
Fluorescent microscopy, following treatment of the ganglion with glyoxylic acid, showed that in both species only the SN1 neurones contained catecholamines. A radioenzymatic assay for dopamine, performed on the locust SN1 neurones, confirmed that this catecholamine was present.
A radioenzymatic assay for 5-hydroxytryptamine (5-HT), performed on both pairs of salivary neurones in the locust, revealed small quantities of this amine in the SN2 neurones, but no significant amount in the SN1 neurones. In the cockroach, 5-HT was assayed in the SN2 neurones only. In contrast to the locust, however, the 5-HT content of these cells was not significantly above that of control cells taken from other ganglia.
These observations demonstrate that only the SN1 neurones are the source of the catecholaminergic fibres investing the locust and cockroach salivary glands. The difference in neurotransmitter content between the SN1 and SN2 neurones suggests that these neurones have separate functions in the control of salivary secretion.
Intracellular pH in the Toad Bufo Marinus Following Hypercapnia
Authors: Snyder Gregory K. , Nestler James R. 
Published: April 2021

ABSTRACT
We investigated the effects of hypercapnia on intracellular acid-base regulation in brain and liver of the toad Bufo marinus L. After 1 h at 5% CO2, arterial PCO2 increased significantly, from 1.6±0.04 to 5.7±0.23kPa, while brain and liver intracellular pH (pHi) decreased significantly. Reductions in pHi of both tissues were partially compensated by increased levels of bicarbonate. Surprisingly, however, compensation was lower than expected in brain and higher than expected in liver. We suggest that compensation in brain may be limited by secondary effects of bicarbonate loading in this tissue.
The Role of Cyclic Amp in the Octopaminergic Modulation of Flight Muscle in the Locust
Authors: Whim Matthew D. , Evans Peter D. 
Published: April 2021

ABSTRACT
The role of cyclic AMP in the octopaminergic modulation of the dorsal longitudinal flight muscles of the locust Schistocerca gregaria has been investigated. Several techniques have been used to elevate cyclic AMP levels in this tissue by mechanisms that bypass the receptor activation stage. These include the use of phosphodiesterase inhibitors to block the metabolism of cyclic nucleotides, the use of forskolin, the diterpene activator of adenylate cyclase, and the direct application of permeable and phosphodiesterase-resistant analogues of cyclic AMP. All these approaches can be shown to mimic the modulatory effects of octopamine on the flight muscle. Surprisingly, the phosphodiesterase inhibitors used were not able to potentiate the actions of octopamine on this preparation. Octopamine increases cyclic AMP levels in a similar fashion in all five motor units of this muscle, an effect that is selectively blocked by phentolamine, an α-adrenergic blocking agent that blocks octopamine receptors in other preparations. In addition, stimulation of the dorsal unpaired median neurone to the dorsal longitudinal flight muscles (DUMDL) results in a frequency-dependent increase in cyclic AMP levels in the muscle that is also blocked by phentolamine. The data presented suggest that the octopamine-mediated modulation of neurally evoked tension in this muscle is brought about by a mechanism that involves an increase in cyclic AMP levels in the tissue.