bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Physical Properties of Spider’s Silk and Their Role in the Design of Orb-Webs
Authors: Denny Mark 
Published: April 2021

ABSTRACT
Determinations were made of several physical properties of the viscid and frame silks of the orb-webs built by the spider Araneus sericatus (Cl.). Both types of silk show a breaking stress of approximately 1 GN/m2 and an initial resilience of approximately 0·35. The breaking extension ratio of viscid silk (λ = 3·00) is much greater than that of frame silk (λ = 1·25), and the viscid silk relaxes to a relatively greater extent. These properties are correlated with the degree of crystallization of the protein from which the silk is made, this factor being controlled by the sequence of amino acids in the protein. The physical properties of the viscid and frame silks allow them to function effectively as shock absorbers and structural elements, respectively; and allow the orb-web to function as an aerial filter with a minimum expenditure of material and energy.
Solute Secretion by the Tube Foot Epithelium in the Starfish Asterias Forbesi
Authors: Prusch Robert D. 
Published: April 2021

ABSTRACT
The K+ and Cl− levels and osmotic concentration of the tube feet fluid in intact starfish (Asterias forbesi) are higher than that in the external sea water or perivisceral (coelomic) fluid. The increase in K+ in the fluid in the tube feet lumen is brought about by the active secretion of K+ by the tube feet epithelium. No exchange of material from the external environment with the more distal portions of the water vascular system across the madreporite was observed in this study. It is suggested that the fluid volume in the tube feet is maintained by active K+ secretion, by the tube feet epithelium, which creates an osmotic driving force for water into the lumen of the tube feet.
The Effect of Prolonged Exercise on the Lateral Musculature of the Brown Trout (Salmo Trutta)
Authors: Davison William , Goldspink Geoffrey 
Published: April 2021

ABSTRACT
Hatchery-reared brown trout (Salmo trutta L.) were exercised continuously for periods of several weeks at swimming speeds of 1·5, 3·0 and 4·5 body lengths/s and their rates of growth were determined. Changes in the major muscle constituents were determined by biochemical analysis and changes in muscle cells using histochemistry and electron microscopy.
At the lowest speed the fish grew much more rapidly, and converted food into fish flesh much more efficiently than their controls kept in still water. Large stores of glycogen and lipid were built up. Gross changes were observed mainly in red muscle cells, with enlargement of the mitochondria being very noticeable.
The fish swimming at intermediate speed showed greater growth than the controls, although the energy expended in swimming against the water current led to an inefficient food conversion rate. Large stores of glycogen were built up, but lipid levels fell, suggesting that this was the major fuel for swimming at this speed. Changes in all the muscle fibre types were observed.
The energy required to maintain the fish in the water flow at the highest speed was so great as to have serious detrimental effects on the fish, and many did not survive. Those which did survive showed signs of gross depletion.
The Significance of Ground Effect to the Aerodynamic Cost of Flight and Energetics of the Black Skimmer (Rhyncops Nigra)
Authors: Withers Philip C. , Timko Patricia L. 
Published: April 2021

ABSTRACT
The kinematics and aerodynamics of flapping and gliding flight by the black skimmer were investigated to evaluate the significance of ground effect to the foraging and daily energy budget of skimmers. Ground effect is an increase in lift and decrease in drag of an aerofoil when close to the ground.
The duration of upstroke and downstroke, the wing movements and the pronation/supination of the wings during flapping flight of the skimmer are similar to other birds. Wing-beat frequency was 3·1 s−1 and flight velocity was 9·1 m s−1. The wing stroke was markedly asymmetric, with the majority of the stroke occurring above the plane of the body. During skimming, wing beats are intermittent and of low amplitude; flight velocity is 10·3 m s−1.
Induced power, parasite power and profile power of skimmers were calculated after Tucker (1973) in the absence of ground effect, and the glide angle and sink velocity were calculated for gliding skimmers. Ground effect was shown to markedly reduce induced power requirements, and hence total power requirement, of flapping flight, and reduce the glide angle and sink velocity during gliding.
The hydrodynamic drag of the lower mandible was estimated to be 10−4 N, which is insignificant compared to the total aerodynamic drag (0·4 N).
Ground effect was shown to markedly increase foraging efficiency and facilitate the attainment of a positive daily energy balance. The significance of ground effect to other flying vertebrates was discussed.
Circadian Rhythm of Output from Neurones in the Eye of Aplysia
Authors: Benson Jack A. , Jacklet Jon W. 
Published: April 2021

ABSTRACT
The compound action potential (CAP) output from the isolated eye of Aplysia, in darkness at constant temperature, exhibits a circadian rhythm of CAP frequency and a circadian rhythm of CAP amplitude when recorded in culture medium for up to two weeks. Deuterated culture medium lengthened the period of the CAP frequency rhythm linearly from 26-7 h in normal culture medium to 33·7 h in 50% D2O culture medium. In 60 % D2O culture medium, the rhythm of CAP frequency was abolished after a single cycle. Lowering temperature had a direct inhibitory effect on the CAP generating mechanism, so that CAP production was virtually abolished below 7 °C. Lowering temperature decreased the amplitude and increased the period of the rhythm, and in eyes maintained at 9·5 °C the rhythm damped out after several cycles. Between 15 and 22·5 °C there was almost complete temperature compensation (Q10 1·07). It is suggested that the CAP generating cells of the eye may be similar in mechanism to central endogenous bursters in Aplysia and other gastropods, and that the circadian rhythm of CAP frequency and CAP burst frequency may be due to a clock-controlled change in frequency of a membrane potential oscillation in the electrotonically coupled secondary neurones.
Circadian Rhythm of Output From Neurones in the Eye of Aplysia
Authors: Benson Jack A. , Jacklet Jon W. 
Published: April 2021

ABSTRACT
The circadian clock that controls CAP frequency was stopped at or near its lowest phase point by long duration cold pulses of 6 °C. On return to normal recording temperature (15 °C), the rhythm was always reinitiated from this phase point. Following long cold pulses, there was often a transient peak of CAP activity lasting 2–6 h. It is thought that this was an effect of rise in temperature after prolonged cooling and not an effect on the clock itself. Twelve h cold pulses, spanning the rhythm peak, caused phase delays. 9 °C pulses caused small delays (e.g. 1·7 h) while large phase delays (e.g. 6·7 h) followed pulses of 5 °C. Some pulses at an intermediate temperature (8·5 °C) caused abnormal post-pulse cycles lasting several days, and resulting in very large phase delays (10-14 h). The abnormal CAP frequency curves following 12 h cold pulses of 8·5 °C spanning the rhythm peak are interpreted as rhythm splits. It is postulated that part of the population of coupled oscillators comprising the circadian clock was slightly delayed by the cold pulse, while the other part was driven further towards the ‘stopped’ state, thus producing a large phase angle difference between the two subpopulations. These drew one another back into phase during several cycles to reform a normal circadian rhythm. It is hypothesized that the circadian oscillations of the two subpopulations did not sum to produce the observed CAP frequency curve; rather the level of CAP output was controlled by whichever subpopulation was discharging at the higher frequency.
Further Evidence for Na/NH4 Exchange in Marine Teleost Fish
Authors: Evans David H. 
Published: April 2021

ABSTRACT
Four species of marine teleosts were shown to possess an external-NH4- inhibited Na uptake from 1 mM-NaCl solutions. The inhibition was not due to changes in the transepithelial potential. Injection of 2 μM-NH4/g fish stimulated Na uptake by Opsanus beta and also stimulated ammonia efflux, 50% of which was dependent upon external Na. The ammonia efflux from three species was partially dependent upon external Na. Na/NH4 exchange in O. beta could be reversed so that 22Na efflux could be stimulated by the addition of 200 mM-NH4 to the external solution. These studies show clearly that marine teleosts possess an Na/NH4 exchange system in sea water which results in a net influx of Na into the fish.
Control of Cuticle Extensibility in the Wings of Adult Manduca at the Time of Eclosion: Effects of Eclosion Hormone And Bursicon
Authors: Reynolds Stuart E. 
Published: April 2021

ABSTRACT
The wings of pharate adult tobacco hornworm moths, Manduca sexta, are relatively inextensible until 3 or 4 h before emergence from the pupal case. At this time the wing cuticle becomes plasticized, so that by the time of eclosion, the wings are readily extensible. This change in the mechanical properties of the wing cuticle is shown to be under the control of a factor from the head. This factor is present in the corpora cardiaca/corpora allata complex, and in the protocerebrum of the brain, being released into the blood prior to eclosion. It is able to act directly on isolated wings. The active principle was found to be indistinguishable in a number of ways from the hormone which triggers emergence from the pupal case, the eclosion hormone. Partial purification of the eclosion hormone failed to separate activity causing eclosion from activity causing wing cuticle plasticization. It is concluded that the same hormone is probably responsible for both effects. The cuticle plasticizing activity of the eclosion hormone forms the basis for a new, highly sensitive bioassay.
Another factor, distinct from the eclosion hormone, is able to cause wing cuticle plasticization. This factor is found in the abdominal nerve cord, and is only released into the blood after eclosion has occurred. It is probably identical with the tanning hormone, bursicon, which is released at this time. The factor in the nerve cord which causes cuticle plasticization is indistinguishable from bursicon in a number of ways, including partial purification by gel filtration. Bursicon evidently causes a further increase in wing cuticle extensibility after eclosion, at the time of wing inflation.
Evidence That Octopus is Colour Blind
Authors: Messenger J. B. 
Published: April 2021

ABSTRACT
Six octopuses were trained on a series of visual discrimination tasks where the discriminanda were presented simultaneously, and where different tasks alternated in a single training session. All the octopuses could make discriminations based on brightness and orientation over the same period of time. Over a period in which all octopuses discriminated a black from a white vertical rectangle none discriminated a yellow vertical rectangle from a grey (of matching brightness). Over a period in which all octopuses discriminated a vertical from a horizontal grey rectangle none discriminated a violet vertical rectangle from a matching grey. The behaviour of the octopuses was qualitatively different in the hue versus grey situations, their attacks being considerably slower and less certain. These results, which agree with previous behavioural findings and a variety of morphological, physiological and biochemical evidence, make it increasingly probable that Octopus vulgaris is colour blind.
The Role of the Cardiac Vagus in the Response of the Dogfish Scyliorhinus Canicula to Hypoxia
Authors: Taylor E. W. , Short S. , Butler P. J. 
Published: April 2021

ABSTRACT
During normoxia, heart rate was governed by a vagal tone which increased at higher acclimation temperatures. This tonic influence was exerted predominantly via the branchial cardiac nerves. The increase in heart rate following atropinization or cardiac vagotomy was associated with a reduction in stroke flow in the ventral aorta in accordance with Starling’s Law of the heart. During slowly induced hypoxia there was a reflex bradycardia, the onset and extent of which varied with acclimation temperature, and which was mediated predominantly via the pair of branchial cardiac vagi. The branchial cardiac vagi were also wholely responsible for the transient marked bradycardia at the onset of rapidly induced hypoxia. Direct measurement of blood flow to the anterior two pairs of branchial arteries demonstrated that they received approximately 37 % of total cardiac output in normoxia and that this proportion was unchanged during hypoxia. The bradycardia during hypoxia in control animals was partially offset by a rise in cardiac stroke volume so that cardiac output decreased slightly. Injection of the adrenergic βreceptor blocker, Propranolol, abolished the increase in stroke flow during hypoxia, but did not effect the bradycardia, and the total blood flow was therefore reduced. The values of during hypoxia from fish acclimated to 17 °C were significantly reduced from the control values following atropinization and either branchial cardiac vagotomy or total cardiac vagotomy. The apparent power output of the heart was reduced during hypoxia at high acclimation temperatures due to the marked bradycardia.
The Relative Importance of Nervous, Humoral and Intrinsic Mechanisms in the Regulation of Heart Rate and Stroke Volume in the DogfishScyliorhinus Canicula
Authors: Short S. , Butler P. J. , Taylor E. W. 
Published: April 2021

ABSTRACTExperiments involving supra-maximal electrical stimulation of the vagus have indicated that the stimulation of the peripheral cut ends of the branchial cardiac branches produces a more intense cardio-inhibition than the stimulation of visceral cardiac branches. It is suggested that the visceral cardiac branches may have a mainly sensory function. In no case could cardioacceleration be obtained during vagal stimulation either before or after injection of atropine, and any increases in stroke volume that occurred accompanied reductions in heart rate. This relationship was considered to be a manifestation of Starling’s Law of the heart and it has been concluded that there is no augmentary sympathetic innervation to the dogfish heart. Evidence also indicates that the Starling relationship is responsible for the increase in stroke volume which accompanies the bradycardia during hypoxia. Circulating catecholamines do not appear to be of importance in this response although they are concerned in cardio-vascular regulation during normoxia.
The Nervous Control of Limb Autotomy in the Hermit Crab Pagurus Bernhardus (L.) and the Role of the Cuticular Stress Detector, CSD1
Authors: Findlay Ian , McVean Alistair 
Published: April 2021

ABSTRACT
Limb autotomy results from the fracture of a preformed breakage plane within the second limb segment. Fracture is produced by the contraction of the large anterior levator (AL) muscle at the same time as its synergist, the posterior levator (PL) muscle. The AL force is thus directed on to a small portion of the breakage plane; withdrawal of this plug initiates cuticular fracture. Autotomy is a response to damage inflicted on the limb. In the absence of sensory information from the second limb segment there is less activity in the units serving the PL. It is shown that stimulation of the sense organ, cuticular stress detector one, provides feedback to PL motor neurones. The feedback is an integral part of the nervous control of limb autotomy.
Estimation of Shunting, Systemic and Pulmonary Output of the Heart, and Regional Blood Flow Distribution in Unanaesthetized Lizards (Varanus Exanthematicus) by Injection of Radioactively Labelled Microspheres
Authors: Berger P. J. , Heisler N. 
Published: April 2021

ABSTRACT
Circulatory parameters in a lizard (Varanus exanthematicus) were determined using the microsphere method. Microspheres (MS) (slightly larger than the erythrocytes and labelled with different γ-emitting isotopes) were injected into a pulmonary vein or the left atrium for determination of the left-to-right (L-R) shunt and the regional distribution of the ventricular systemic output. Injections were also made into the sinus venosus for determination of the right-to-left (R-L) shunt. The relative blood flow was obtained as the ratio of the MS activity found in the various tissues over the total activity injected. Absolute calibration of the method was performed by introduction of an ‘artificial organ’into the circulatory system (Hales, 1973).
Ventricular systemic output (VSO), in five animals, averaged 121 ml/ (min.kg) and ventricular pulmonary output 119 ml/(min.kg). The value of VSO was significantly higher than those observed in other lizard species. In all experimental animals both R-L as well as L-R shunting of various extent occurred. The reliability of the microsphere method as applied in lizards is discussed and is considered to be relatively accurate even under conditions of incomplete mixing of shunted and unshunted blood in systemic heart output.
The Influence of Diet, Age and State of Hydration on Na+, K+ and Urate Balance in the Fat Body of the Cockroach Periplaneta Americana
Authors: Tucker Lois E. 
Published: April 2021

ABSTRACT
The effect of diet, age, sex and state of hydration on the relationship between Na+, K+ and urate in the fat body tissue of the cockroach Periplaneta americana has been investigated. There is a significant correlation between K+ and urate concentrations in the fat bodies of both males and females in late nymphal and adult stages. Animals fed on a dextrin/casein diet, which had a K+ content of about one-third that of the rat pellets normally used for food, had a lower than normal K+/urate ratio. In both the normally fed and dextrin/casein-fed groups of animals, dehydration caused a decrease in the K+/urate ratio. Dehydration (and starvation) caused an increase in the amount of urate per unit weight of fat body. Some of the urate in the fat body is present in small spherical cellular inclusions. There is also a correlation between the K+ concentration and the number of spherules. The ratio of spherules/urate is significantly higher in hydrated animals than in dehydrated ones.
Respiratory and Cardiovascular Responses of the Pigeon to Sustained, Level Flight in A Wind-Tunnel
Authors: Butler P. j. , West N. H. , Jones D. R. 
Published: April 2021

ABSTRACT
Five pigeons were trained to fly in a boundary-layer wind-tunnel at a velocity of 10 m s−1 for at least 10 min, and a number of respiratory and cardiovascular variables were recorded. For comparison, heart rate, respiratory frequency and E.M.G. from the pectoralis major muscles were also recorded, using radio-telemetry, from free-flying pigeons. For the flights in the wind tunnel there were immediate increases in respiratory frequency and heart rate upon take-off; these variables continued to increase during the flight, eventually becoming on average 411 breaths min−1 (20 × resting) and 670 beats min-1 (6 × resting) respectively. There was a 1:1 relationship between ventilation and wing beat. Oxygen uptake and carbon dioxide production reached their highest values of 12·5 × and 14·4 × resting respectively within 1 min of take-off and then declined to steady levels of 200 ml kg−1 min S.T.P.D. (1O × resting) and 184 ml kg−1 min S.T.P.D. (10·7 × resting) 4 min after take-off. If allowances are made for the weight and drag of the mask and tubes, these stable values are at least 12 % higher than would occur in an unloaded bird. Body temperature rose steadily after take-off, reaching a stable value of 43·3 °C, which was 2 °C above resting, after 6 min of flight. There was a 1·8 × rise in content difference and little change in cardiac stroke volume during night, so that the rise in heart rate was the major factor in transporting the extra O2 to the active muscles. Respiratory quotient rose from 0·85 at rest to 0·99, 30 s after take off, and then fell to 0·92 after 7 min of flight. Blood lactate rose to 59·8 mg% (6·5 × its resting value). Comparisons with the free-flying birds indicated that the pattern of flight in the wind tunnel was somewhat abnormal, especially at the beginning of a flight, and this may account for the value of being higher at the start of a flight and then declining to a steady value as the flight progressed. Upon landing, heart rate, and body temperature began to fall immediately, and within 2 min, heart rate, and had returned to the ‘tunnel on’ resting values. Respiratory frequency increased upon landing and its decline closely matched the fall in body temperature. R.Q. rose above unity immediately upon landing as CO2 was removed in excess of its metabolic production, and then fell below the resting value as CO2 was retained, presumably to maintain acid/base balance during the metabolism of lactic acid.
The Influence of Age, Diet and Lipid Content on Survival, Water Balance and Na+ and K+ Regulation in Dehydrating Cockroaches
Authors: Tucker Lois E. 
Published: April 2021

ABSTRACT
In dehydrating conditions late instar nymphs lose weight more slowly and survive longer than adult Periplaneta americana. This appears to be due, at least in part, to the larger lipid stores which are found in the fat bodies of the nymphs. When the water loss from an animal is greater than the amount of metabolic water obtained from the catabolism of stored foods, water is removed from the haemolymph in order to maintain water balance in the tissues. Dehydration for 6 days causes the haemolymph volume to decrease markedly in most adults, but the haemolymph Na+ and K+ concentrations increase only slightly. During dehydration the mean Na+/K+ ratio of the fat body tissue increased in adults, except in those which had been fed on pure carbohydrate prior to dehydration. Although not always statistically significant on account of the large variances, the changes in mean Na+, K+ and in the Na+/K+ ratio suggest there is an increase in Na+ and decrease in K+ in the fat body of animals where the haemolymph volume is markedly reduced by dehydration.
Regulation of Ions in the Haemolymph of the Cockroach Periplaneta Americana During Dehydration and Rehydration
Authors: Tucker Lois E. 
Published: April 2021

ABSTRACT
Experiments using 22Na-uptake and serial sampling techniques showed that during dehydration Na was taken up by the fat body in adult Periplaneta americana, but not in nymphs. Generally, accumulation of Na in the fat body was highest in animals which had little reserve lipid and in those which excreted the smallest amounts of Na during the dehydration period.
Dehydration caused little change in the Cl− concentration in the haemolymph. From results of 36Cl-uptake experiments, it appears that the fat body is not involved in the regulation of haemolymph Cl− during dehydration. In old adults, the hindgut was the tissue in which dehydration caused the greatest increase in 36C1 uptake.
The mechanisms which enable cockroaches to withstand dehydrating conditions are discussed.