bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pituicytes, Glia and Control of Terminal Secretion
Authors: Hatton Glenn I. 
Published: April 2021

ABSTRACT
Once thought to be hormone-synthesizing cells, the pituicytes are now known to be the resident astroglia of the neurohypophysis (also referred to here as the posterior pituitary). Early investigators interpreted light microscopic observations as demonstrating pituicyte secretion, since pituicytes appeared to contain neurosecretory material when hormone demand was low and not when it was increased. Ultrastructural studies have shown that pituicytes actually engulf or completely surround neurosecretory axons and axonal endings under basal conditions, and release these neural processes when conditions require increased hormone output. Thus, the pituicytes appeared to the early workers to contain and release hormone when they actually contained and released axons and terminals in which the hormone was, in fact, contained. Dynamic interactions of pituicytes with various of the other elements in the gland have also been demonstrated. When hormone demand is low, the pituicytes not only engulf the neurosecretory processes but also interpose their own processes between the secretory endings and the basal lamina. Since any hormone that is secreted must pass through the basal lamina and into the perivascular spaces in order to enter the fenestrated capillaries, pituicyte interpositions form physical, and perhaps chemical, barriers to hormone entering the circulation. Increasing hormone demand results in retraction of pituicyte processes from the basal lamina, permitting increased neural contact. Studies of isolated neurohypophysis and of cultured adult rat pituicytes have shown that these glia undergo appropriate morphological changes in response to osmotic stimuli or to receptor-mediated activation of adenylate cyclase. Both these events are thought to be effectors of the alterations seen in vivo. Some possible mechanisms by which pituicytes may participate in the control of secretory events are discussed.
Capturing and Quantifying the Exocytotic Event
Authors: Morris John F. , Pow David V. 
Published: April 2021

ABSTRACT
Although exocytosis is now known to be the universal method by which proteins are released from eukaryotic cells, we know surprisingly little of the mechanism by which exocytosis occurs. One reason for this is that it has proved difficult to capture sufficient of these evanescent events to permit their study. The difficulty with which exocytoses can be visualized with standard preparative techniques varies among tissues, but the problem is particularly apparent in the mammalian nervous system.
Tannic acid has recently been introduced as an agent by which exocytosed granule cores can be captured and visualized electron-microscopically. Application of tannic acid to the magnocellular neurosecretory system reveals exocytoses from all parts of their terminal arborization within the neural lobe, and also from their dendrites within the hypothalamus. Quantification of the exocytoses in unstimulated tissue and in tissue stimulated by a variety of exogenous and endogenous mechanisms indicates: (a) that exocytosis occurs equally from each unit of membrane of the perivascular nerve endings, and of the axonal swellings that were previously thought to be sites of granule storage, rather than release; (b) that, in the nerve endings, a greater proportion of the stored granules are exocytosed, and thus the endings are specialized for release not by any particular property of their membrane, but by a high surface membrane:volume ratio. Together, the data cast doubt on the hypothesis that exocytosis occurs only at some functionally specialized sites at certain loci in the membrane. Rather, the data favour the hypothesis that magnocellular granules can fuse with any part of the membrane, depending on constraints imposed by the cytoskeleton, and a local increase in cytosolic free calcium level.
When applied to hypothalamic central nervous tissue, tannic acid reveals that exocytosis of dense-cored synaptic vesicles occurs preferentially, but not exclusively, at the membrane apposed to the postsynaptic element. However, about half of all exocytoses from synaptic boutons occur at bouton membrane unrelated to the synaptic cleft.
In all tissues studied, tannic acid reveals a heterogeneity among secretory cells in the extent of exocytosis that occurs in response to stimulation, and permits an analysis of the degree to which secretion is polarized in any one direction.
These results question long-held assumptions concerning the site at which neurones release transmitters and modulators. Tannic acid seems likely to prove a potent tool in the investigation of both the mechanism of exocytosis and the ways in which different types of cells adapt the process to perform their physiological functions.
A Note on the Permeability of Trout Eggs to D2O AND H2O
Authors: Krogh August , Ussing Hans H. 
Published: April 2021

ABSTRACT
Gray showed (1932) that the “vitelline membrane” of the trout’s egg is normally impermeable both to water and salts, while the tough “chorion” is freely permeable. In view of the fact that the eggs when squeezed out from the fish are somewhat permeable to water (Irving&Manery, 1934) and swell up to a certain extent and that the methods used by Gray might fail to reveal a very low grade of permeability, we found it worth while to utilize the “heavy” water now available for the study of permeability problems (Hevesy et al., 1935) for a few supplementary experiments on trout eggs.
Pseudo-Rheotropism in Fishes
Authors: Gray J. 
Published: April 2021

ABSTRACT
Many species of pelagic fish tend to orientate their bodies so that their heads are directed upstream, and to maintain a fixed position in space although the surrounding water is in motion relative to the earth. As pointed out by Lyon (1904, 1909), it is impossible to attribute these phenomena to direct stimulation of the fish by the surrounding water, for they may occur under conditions in which there is no relative motion between the fish and its surrounding medium. Lyon showed that under normal circumstances certain fish orientate themselves by optical stimuli ; if such an animal is moved passively—either by a current of water or any other means—it responds by movements which are so adjusted as to maintain a stationary optical field ; in other words, any passive movement between the fish and its visual field calls forth compensatory movements equal and opposite to the passively induced motion. Although such phenomena undoubtedly occur in nature it is doubtful whether optical stimulation accounts for all the phenomena usually included under the term “rheotropism”. Both Steinmann (1914) and Schiemenz (1927) have shown that, in the absence of a moving visual field, fish show a marked tendency to maintain a fixed position in space when subjected to rotary movements on a turn-table. Steinmann rightly associated this behaviour with the activity of the semicircular canals of the labyrinth, but his interpretation also involves the belief that the relative motion of the fish and the water can be influenced by the motion of the water relative to the ground. This conclusion was very properly rejected by Schiemenz, who concluded that orientation was effected by an “unanalysierte Fähigkeit die Drehung an sich zu perzipieren”.
A New Form of Micro-Respirometer; With A Note on the Effect of Cleavage on the Respiration of the Egg ofRana
Authors: Stefanelli Alberto 
Published: April 2021

ABSTRACTIn order to observe the respiration of single egg-cells it seemed desirable to construct a respirometer of greater sensitivity than those designed by Barcroft (1908) or Warburg (1926), or than that of any of the various modifications of these two instruments (Novy et al. 1925 ; Thunberg, 1905 ; Winterstein, 1911 ; Fenn, 1927–8 ; Fraps, 1930; and Krüger, 1934).
The Humidity Reactions of the African Migratory Locust,Locusta Migratoria MigratorioidesR. & F., Gregarious Phase
Authors: Kennedy John S. 
Published: April 2021

ABSTRACTUnder the conditions of the experiments described, Locusta migratoria migratorioides shows a preference for dry air in all parts of the humidity range, although dry air is by no means optimal for development, maturation, and breeding. The strength of the reaction is correlated with the magnitude of the humidity difference available, but appears to be little dependent on the region of the humidity range. The mechanism of the reaction is hygrokinetic and possibly hygrophobotactic as well, but probably not hygrotropotactic.
The Gill Movements of NymphalEcdyonurus Venosus(Ephemeroptera) and the Currents Produced by Them in Water
Authors: Eastham L. E. S. 
Published: April 2021

ABSTRACTWith further reference to the phenomena of mayfly gill movement (Eastham, 1932, 1934, 1936), an examination of the gills of Ecdyonurus venoms has been made.The methods adopted for analysing gill movement and for observing the currents were similar to those employed for Caenis and Leptophlebia (Eastham, 1934, 1936) and need not be described here. It is perhaps sufficient to remark that the gills may be induced to oscillate at the rate of about seven per second thus making observation by means of the stroboscope possible (Gray, 1930).
The Dependence of Head Curvature on the Development of the Heart in the Chick Embryo
Authors: Waddington C. H. 
Published: April 2021

ABSTRACT
At about the end of the second day of incubation, the anterior end of the embryonic axis of an embryo chick becomes twisted and bent. The twist, which is a simple rotation around the main embryonic axis, brings the left side of the head in contact with the yolk and raises the right side to point vertically upwards. The bending throws the embryonic axis into a rather complicated shape, the essential feature of which is that the anterior tip of the head remains comparatively near to a point just posterior to the ears, while the whole region of neural tube and brain which lies in between these two points is bent into an arc. The posterior part of the arc curves out slightly to the left of the main line of the embryonic axis but much the greater part lies to the right of this line. In the concavity of the curve, on the right side, lies the heart.
A Note On the Chitinous Nature of the Peritrophic Membrane ofMelanoplus BivittatusSay
Authors: Brown A. W. A. 
Published: April 2021

ABSTRACTA Previous communication (Brown, 1937) reported that the excreta of Melanoplus, after treatment by Campbell’s quantitative method for the estimation of chitin, yielded a residue which possessed a very low nitrogen content; it was suggested therefore that the peritrophic membrane here was not chitinous. Re-examination of this material showed, by the blue colour given with I2 and 75 per cent H2SO4, that its content of cellulose was very considerable; the chitinous portion, as indicated by the violet colour with I2 and 1 per cent H2SO4, consisted of small peripheral elements. This cellulose could be left behind by converting the chitin to chitosan, and extracting the latter in 3 per cent acetic acid (Hoppe-Seyler, 1894).
Studies on the Growth of TissuesIn Vitro
Authors: Jacoby F. , Trowell O. A. , Willmer E. N. 
Published: April 2021

ABSTRACTIt has already been shown (1933, 1936) that chick fibroblasts (mesenchyme cells derived from the heart or from periosteal tissue) can be reduced to a state in which growth by cell division is almost at a standstill and that, by the addition to the medium of embryo tissue juice, the cells can be caused to divide again. The higher the concentration of embryo juice used, the greater is the number of cell divisions which occur. The addition of the embryo juice is followed within the first 2 hours by increased movement of the cells, which reaches its maximum in about 10 hours, but it is not until this latter time that cell divisions begin again.
The Spherical form of the Mammalian Erythrocyte
Authors: Ponder Eric 
Published: April 2021

ABSTRACTIn a number of papers, I and my collaborators have considered various methods for measuring the volume of mammalian red cells, either in the discoidal 1 or in the spherical form (Ponder & Saslow, 1930a, b, 1931; Macleod & Ponder, 1933; Ponder & Robinson, 1934; Ponder, 1935 a, b). Some of these methods, such as the diffraction method, are applicable to spheres only, and others measure only changes in volume such as occur in hypotonic media. So far as this paper is concerned, the two most important conclusions of the investigations are (a) that the transformation from disk to sphere, whether effected by the addition of lecithin or one of the photodynamic dyes (Ponder, 1936), or by enclosing the cells between two closely opposed surfaces (Ponder, 1928-9), is accompanied by no change in volume, and (b) that at the “critical tonicity” in which haemolysis begins in hypotonic media, the percentage increase in volume is substantially the same irrespective of whether the cells are disks or spheres.
Permeability of Sanddollar Ova and ofModiolusandMytilusGills to Various Acids and Their Salts
Authors: Beck Lyle V. , Chambers Robert 
Published: April 2021

ABSTRACTThe pH indicator, methyl red, as a vital stain (from a medium at pH 5.3) and having a relatively low pK value, was used for testing the penetration of acids and of salts of organic acids into cells. The cells were those of gill strips of Modiolus and Mytilus and the fertilized eggs of the sanddollar, Echinarachnius parma. The penetration of various acids into cells was studied by immersing the cells in artificial, unbuffered sea water acidified with the given acid at 3 ×10−3M concentration in experiments with gill strips and at 10 × 10−3M concentration in experiments with sanddollar eggs. The colour change indicating intracellular acidification was almost instantaneous with benzoic acid (5 sec. or less), slightly less rapid (5–20 sec.) with the fatty acids, valeric to acetic, and slow with HCl. The rate of the return of the methyl red to the original alkaline colour upon the transfer of the cells to artificial acid sea water (pH 5.3) was in the same order for the various acids. Intracellular acidification with a fatty acid was diminished when salts of the acid were present in the medium. Since the counteracting effect of the salts does not appear until the concentration of these salts exceeds that of the fatty acid by at least three times we may conclude that when both acid and salt are penetrating, the acid does so more rapidly than its salts. The penetration of salts of acetic, butyric and benzoic acids also occurred in the absence of added acid and at an alkaline pH approximating that of normal sea water. However, the rate of penetration was much slower than in the presence of added acid. Evidence for penetration of the salts in absence of added acid was obtained by exposing the cells to the salts prior to treatment with the corresponding acid. Effects obtained by prior treatment with the salts alone were enhanced by increasing the concentration of potassium in the medium.
The Behaviour of Epiblast Grafts Beneath the Primitive Streak of the Chick
Authors: Abercrombie M. 
Published: April 2021

ABSTRACTGrafts consisting of area opaca ectoderm, presumptive epidermis, presumptive neural tissue, or presumptive mesoderm (axial or side-plate), were transplanted to a position immediately under the primitive streak of chick blastoderms in the primitive streak stage. The grafts, though they sometimes remained as a non-neural epithelium, were usually neurally induced, contemporaneously and co-extensively with the neural induction of the host. The graft-derived neural tissue is often much thicker than the host neural tissue, and though usually forming an autonomous structure, it is frequently arranged with a high degree of symmetry relative to the host. If, however, the graft remains for a long time uninduced, lying in the host mesenchyme, it tends to break up into mesenchyme itself. It is probable that all parts of the epiblast, whatever their presumptive fate, are competent to form neural tissue, provided their epithelial structure is maintained ; and it is notable that this is true of presumptive mesoderm. The dorso-ventral polarity of the grafts is maintained whatever their orientation in the host; but the irreversible determination of this polarity was probably not tested. The antero-posterior polarity of the grafts was without effect on their differentiation. An elongation of the graft along the antero-posterior axis of the host usually occurred. It was often very marked, and generally consisted in the posterior end of the graft accompanying the host primitive node as it moved backwards. It is believed to be due to the induction of an active movement in the graft itself. The host is considerably modified by the presence of the graft. In particular, the head-fold is usually suppressed. The formation of the foregut is frequently upset, but the closed foregut shows a considerable power of regulation.
The Behaviour of Grafts of Primitive Streak Beneath the Primitive Streak of the Chick
Authors: Abercrombie M. , Waddington C. H. 
Published: April 2021

ABSTRACTGrafts consisting of pieces of primitive streak from blastoderms in the primitive streak stage were placed under the primitive streak of blastoderms also in this stage. Various effects of the host on the graft are described, particularly the reversal of the antero-posterior orientation of the graft, the alteration of the regional character of the graft so as to conform with the host tissues at the same level, the suppression of differentiation in the posterior end of the primitive streak, and the incorporation of the graft tissues into the host. A considerable number of inductions occurred, since the host axis often apparently shifts to one side of the graft. The inductions are of two kinds, the normal evocation by graft mesoderm, resulting usually in the formation of superfluous neural tissue; and the complementary induction of a normal secondary axis, which it is supposed is most often due to the preliminary induction of a primitive streak in the host. Various effects of the graft on the host occur. In particular the disturbance of the head mesenchyme suggests that foregut diverticula are produced where head mesenchyme joins lateral plate mesothelium.
Conversion of Presumptive Ectoderm to Mesoderm in the Chick
Authors: Waddington C. H. , Taylor Jean 
Published: April 2021

ABSTRACTFragments of epiblast, or of epiblast together with endoderm, were placed in holes cut in the primitive streaks of young chick embryos, and the embryos then cultivated in vitro for about 24 hours. The grafts were sometimes extruded, but in many cases they healed more or less well. In those cases in which partial healing occurred the grafted presumptive ectoderm has usually developed into mesodermal structures, such as somites, though in a few cases it has been induced to form neural tissue. In some cases healing was so complete that no trace of the graft can be found, and in these embryos also the greater part of the presumptive ectoderm must have formed mesoderm. The conversion of presumptive ectoderm into mesoderm has only been accomplished by the method of the above experiments, which involves the performance by the graft of the normal gastrulation movements. In the Amphibia the performance of such movements is unnecessary, and it is suggested that in the chick the importance of the movements is not that they are a part of the gastrulation process but merely that they involve the breakdown of the epithelial structure of the grafted ectoderm. The relevance of these results to the germ-layer theory is discussed, and it is pointed out that, although it is clear that there is no fundamental physiological distinction between the ectoderm and mesoderm before invagination, it is still possible that such a distinction may exist between the endoderm and the ectodermmesoderm system.
The Water and Electrolyte Exchange ofNereis Diversicolor(Müller)
Authors: Ellis W. G. 
Published: April 2021

ABSTRACTIt has been shown by McCutcheon & Lucke (1928) that in glucose solutions isotonic with 40 per cent sea water, the eggs of the sea-urchin Arbacia absorb twice as much water as they do from 40 per cent sea water, and that this increased imbibition is prevented by a small concentration of calcium ion in the glucose solution, even in the absence of the other cations of sea water. Pantin (1931 a) showed that the Platy-helminth, Procerodes (Gunda) ulvae, which in its estuarine habitat withstands tidal changes in osmotic pressure, is only able to survive in very dilute salt solutions if these contain calcium.
The Toxicity of Dissolved Metallic Salts toPolycelis Nigra(Muller) andGammarus Pulex(L.)
Authors: Jones J. R. Erichsen 
Published: April 2021

ABSTRACTA brief review is given of previous work on the toxic effect of aqueous solutions of metallic salts on living protoplasm and fresh-water animals. The behaviour of Polycelis nigra in aqueous solutions of metallic salts is described, survival curves for this animal in some variety of salts are given, and the mode of toxic action of these salts is discussed. It is shown that in the case of heavy metal salts the toxic effect at concentrations below isotonicity is due almost entirely to the cation, the toxicity of the anion being relatively small. At concentrations above isotonicity the anion and the osmotic pressure of the solution act as additional lethal factors. Salts of the metals of the alkalis and alkaline earths are shown to be comparatively harmless below isotonicity, with the exception of salts with a toxic anion such as potassium chromate. This salt is highly toxic at low concentrations. It is shown that in the case of the nitrates and sulphates of the heavy metals, the toxicity is determined by the product of the normality and the electrical conductance ratio at that normality. Recovery experiments with Polycelis are described and it is shown that these illustrate the above relationship between toxicity and conductivity. Survival curves for Gammaruspulex in salts of copper and zinc are described. Those for zinc exhibit the same relationship.
Wound Healing in an Insect (Rhodnius ProlixusHemiptera)
Authors: Wigglesworth V. B. 
Published: April 2021

ABSTRACTIf the epidermis of an animal is injured so that its continuity is destroyed, the surrounding cells multiply and spread over the wound until the gap is filled. Then their growth ceases. The factors which initiate this renewed growth of “repair”, and the factors by which growth is arrested when the defect has been made good, are very incompletely known. The object of the present work was to re-investigate this old problem upon new material.
Stretch Receptors in the Muscles of Fishes
Authors: Fessard A. , Sand A. 
Published: April 2021

ABSTRACTThe presence of stretch receptors in the muscles of Raja and Scylliwn has been physiologically demonstrated. Their morphology is unknown. The behaviour of a single end-organ in the radial muscles of the pelvic fin of Raja clavata has been examined in detail. The adaptation curve and the tension-frequency relationship have been determined. Under constant tension a single end-organ has continued to function rhythmically for over 1 hour. When tension is suddenly reduced, there follows a silent period before the frequency of discharge corresponding to the reduced tension appears. The quantitative aspects of the behaviour of the stretch receptor of Raja bear a closer resemblance to those of the receptors of the carotid sinus than to those of mammalian and amphibian limb muscles. The response of muscle receptors during a passive undulatory movement of the pectoral fin has been recorded, and their role in the swimming rhythm is discussed.