SUPPRESSION OF PHOTOTROPIC CIRCUS MOVEMENTS OF LIMAX BY STRYCHNINE

By injection with strychnine the phototropic circus movements of the slug Limax maximus may be suppressed, its phototropism abolished. The creeping activity of the foot is not in any essential way interferred with. Strychnine produces in Limax central nervous effects of the sort associated with its characteristic action. Hence, although an effect of the drug upon photoreceptors cannot be definitely excluded, the experimental result is held to demonstrate that in orientation during circus movements there occurs central "competition" between impulses resulting (1) in the release of pedal waves and (2) in the maintenance of a turning posture.     

THE PHOTOTROPIC EXCITATION OF LIMAX

The photic orientation of Limax creeping geotropically upon a vertical plate is such that the phototropic vector determining the angular deflection β from the vertical path is proportional to log I. This is proved by the fact that with horizontal illumination tan β is directly proportional to log I; with non-horizontal light rays from a small source the ratio See PDF for Equation is directly proportional to log I (where A = the angle between light rays and the path of orientation), the vector diagram of the field of excitation being in this case not a right-angled triangle.     

THE LOCOMOTION OF LIMAX : I. TEMPERATURE COEFFICIENT OF PEDAL ACTIVITY.

Pedal progression of the slug Limax maximus was studied to obtain relations between wave velocity on the sole of the foot, wave frequency, the advance due to a single wave, and the velocity of vertically upward creeping. Each of the first three quantities is directly proportional to the simultaneous velocity of progression. Under comparable conditions, that is when work is done at a constant rate, the frequency of pedal waves is influenced by the temperature according to the equation of Arrhenius, with µ = 10,700 (Q ₁₀ for 11° to 21° = 2.1). The velocity of a single wave must have very nearly the same "temperature characteristic," which is found also in another case of nerve net transmission (in Renilla).     

Phototropic response features for different systematic groups of mesoplankton under adverse environmental conditions

Current trends in the application of bioindication methods are related to the use of submersible tools that perform real‐time measurements directly in the studied aquatic environment. The methods based on the registration of changes in the behavioral responses of zooplankton, in particular Crustaceans, which make up the vast majority of the biomass in water areas, seem quite promising. However, the multispecies composition of natural planktonic biocenoses poses the need to consider the potential difference in the sensitivity of organisms to pollutants.This paper describes laboratory studies of the phototropic response of plankton to attracting light. The studies were carried out on a model natural community that in equal amounts includes Daphnia magna, Daphnia pulex, and Cyclops vicinus, as well as on the monoculture groups of these species. The phototropic response was initiated by the attracting light with a wavelength of 532 nm close to the local maximum of the reflection spectrum of chlorella microalgae. Standard potassium bichromate was used as the model pollutant.The largest phototropic response value is registered in the assemblage. The concentration growth rate of crustaceans in the illuminated volume was 4.5 ± 0.3 ind (L min)⁻¹. Of the studied species, the phototropic response was mostly expressed in Daphnia magna (3.7 ± 0.4 ind (L min)⁻¹), while in Daphnia pulex, it was reduced to 2.4 ± 0.2 ind (L min)⁻¹, and in Cyclops vicinus, it was very small—0.16 ± 0.02 ind (L min)⁻¹. This is caused by peculiar trophic behavior of phyto‐ and zoophages. The addition of a pollutant, namely potassium bichromate, caused a decrease in the concentration rate of crustaceans in the attracting light zone, while a dose‐dependent change in phototropic responses was observed in a group of species and the Daphnia magna assemblage.The results of laboratory studies showed high potential of using the phototropic response of zooplankton to monitor the quality of its habitat thus ensuring the early diagnostics of water pollution. Besides, the paper shows the possibility of quantifying the phototropic response of zooplankton using submersible digital holographic cameras (DHC).     

WAVE LENGTH OF LIGHT AND PHOTIC INHIBITION OF STEREOTROPISM IN TENEBRIO LARV?

A definite intensity of white light is required (about 136 m.c.) to produce negative phototropic orientation of creeping Tenebrio larvæ away from contact with a vertical glass surface. This gives a measure of stereotropism in terms of phototropism, or reciprocally. The effectiveness of light for the suppression of stereotropism varies with wave length. It is therefore simple to obtain a measure of the relation between wave length and stimulating efficiency in this case of phototropic orientation. By determinations of the minimal energy required to inhibit stereotropism with different regions of the spectrum, it is found that the maximum effectiveness is sharply localized in the neighborhood of 535µµ. The curve connecting stimulating efficiency with wave length, while giving a picture of the effective absorption by the photosensory receptors, probably does not permit accurate characterization of the essential photosensitive material.     

Steady-State Phototropism in Phycomyces

The steady-state phototropic bending of Phycomyces sporangiophores was studied using apparatus designed to keep the growing zone vertical and the angle of illumination constant over long periods of time. The bending speed is quite constant if the intensity and angle of illumination are fixed. A phototropic inversion occurs in response to a sudden change in intensity, either an increase or a decrease. A bending component lateral to the illumination direction is strongly evident at normal incidence. It is shown that this component is due to a rotation between the stimulus and response loci about the axis of the growing zone, which is probably related to the spiral growth of the cell. The steady-state bending speed is at a maximum value for illumination directions ranging from normal incidence to about 45°. From 45 to 14° the bending speed decreases linearly with angle, reaching zero at 14°. Angles less than 14° elicit a weak negative phototropic response. Using an optical model of the growing zone, the intracellular intensity distribution was determined as a function of the angle of illumination. Several hypotheses relating the intensity distribution to the phototropic response are discussed.     

TEMPERATURE CHARACTERISTICS FOR SPEED OF MOVEMENT OF THIOBACTERIA

The speed of translatory movement of Beggiatoa alba is governed by temperature in such a way that between 5° and 33° the temperature characteristics µ = 16,100 and µ = 8,400 respectively obtain for the temperature ranges 5° to 16.5° and 16.5° to 33°. The "break" at 16°–17° is emphasized by the occurrence of a wider latitude of variation in speed above this temperature. Above 16° the progression of Thiothrix yields µ = 8,300. The possible relation of these values to that previously obtained for similar movement in (photosynthetic) Oscillatoria is commented upon.     

THE RELATIONS OF TEMPERATURE TO THE POTASSIUM EFFECT AND THE BIOELECTRIC POTENTIAL OF VALONIA

The effect of temperature upon the bioelectric potential across the protoplasm of impaled Valonia cells is described. Over the ordinary tolerated range, the P.D. is lowest around 25°C., rising both toward 15° and 35°. The time curves are characteristic also. The magnitude of the temperature effect can be controlled by changing the KCl content of the sea water (normally 0.012 M): the magnitude is greatly reduced at 0.006 M KCl, enhanced at 0.024 M, and greatly exaggerated at 0.1 M KCl. Conversely, temperature controls the magnitude of the potassium effect, which is smallest at 25°, with a cusped time course. It is increased, with a smoothly rising course, at 15°, and considerably enhanced, with only a small cusp, at 35°. A temporary "alteration" of the protoplasmic surface by the potassium is suggested to account for the time courses. This alteration does not occur at 15°; the protoplasm recovers only slowly and incompletely at 25°, but rapidly at 35°, in such fashion as to make the P.D. more negative than at 15°. This would account for the temperature effects observed in ordinary sea water.     

ON THE MECHANISM OF TONIC IMMOBILITY IN VERTEBRATES

1. The durations of successive periods of induced tonic immobility in the lizard Anolis carolinensis was examined as a function of temperature. An automatic recording method was employed and observations were made of 12,000 to 15,000 immobilizations with six animals over a temperature range of 5° to 35°C. during 5 months. 2. The durations of the immobile periods were found to vary rhythmically in most cases. The reciprocal of the duration of the rhythm, i.e., the rate of change of the process underlying the rhythms, when plotted as a function of temperature according to the Arrhenius equation show distributions of points in two straight line groups. One of these groups or bands of points extends throughout the entire temperature range with a temperature characteristic of approximately µ = 31,000 calories, and the other covers the range of 20° to 35°C. with µ equal to approximately 9,000 calories. 3. The initial stimulus in a series of inductions of immobility appears to set off a mechanism which determines the duration of the state of quiescence. Succeeding forced recoveries seem to have no effect on the normal duration of the rhythm. 4. These results are interpreted by assuming the release, through reflex stimulation, of hormonal substances, one effective between 5° and 35°C. and the other effective between 20° and 35°C. These substances are assumed to act as selective inhibitors of impulses from so called "higher centers," allowing impulses from tonic centers to pass to the muscles. 5. In some experiments a progressive lengthening in successively induced periods of immobility was observed. The logarithm of the frequency of recovery when plotted against time in most of these cases (i.e., except for a few in which irregularities occurred) gave a linear function of negative slope which was substantially unaffected by temperature. In these cases it is assumed that a diffusion process is controlling the amount of available A substance. 6. The results are similar to those obtained by Crozier with Cylisticus convexus. The duration of tonic immobility seems to be maintained in both arthropod and vertebrate by the chemical activity of "hormonal" selective inhibitors. The details of the mechanisms differ, but there is basic similarity. 7. Injections of small amounts of adrenalin above a threshold value are found to prolong the durations of tonic immobility of Anolis, by an amount which is a logarithmic function of the "dose." It is possible that internally secreted adrenalin, above a threshold amount, may be involved in the maintenance of tonic immobility. 8. The production of tonic immobility reflexly is a problem distinct from that of the duration of immobility. It is suggested that the onset may be induced by "shock" to the centers of reflex tonus causing promiscuous discharge of these centers with accompanying inhibition of the higher centers. Such a condition may result when an animal is suddenly lifted from the substratum and overturned, or when, as in the case of Anolis, it struggles with dorsum down. This reaction of the "tonic centers" may at the same time lead to discharge of the adrenal glands by way of their spinal connections thus prolonging the state.     

HYDROSTATIC PRESSURE AND TEMPERATURE IN RELATION TO STIMULATION AND CYCLOSIS IN NITELLA FLEXILIS

Nitella flexilis cells are not stimulated to "shock stoppage" of cyclosis by suddenly evacuating the air over the water or on sudden readmission of air, or on suddenly striking a piston in the water-filled chamber in which they are kept with a ball whose energy is 7.6 joules, provided the Nitella cell is not moved by currents against the side of the chamber. Sudden increases in hydrostatic pressure from zero to 1000 lbs. or 0 to 5000 lbs. per square inch or 5000 to 9000 lbs. per square inch usually do not stimulate to "shock stoppage" of cyclosis, but some cells are stimulated. Sudden decreases of pressure are more likely to stimulate, again with variation depending on the cell. In the absence of stimulation, the cyclosis velocity at 23°C. slows as the pressure is increased in steps of 1000 lbs. per square inch. In some cells a regular slowing is observed, in others there is little slowing until 4000 to 6000 lbs. per square inch, when a rapid slowing appears, with only 50 per cent to 30 per cent of the original velocity at 9000 lbs. per square inch. The cyclosis does not completely stop at 10000 lbs. per square inch. The pressure effect is reversible unless the cells have been kept too long at the high pressure. At low temperatures (10°C.) and at temperatures near and above (32°–38°C.) the optimum temperature for maximum cyclosis (35–36°C.) pressures of 3000 to 6000 lbs. per square inch cause only further slowing of cyclosis, with no reversal of the temperature effect, such as has been observed in pressure-temperature studies on the luminescence of luminous bacteria. Sudden increase in temperature may cause shock stoppage of cyclosis as well as sudden decrease in temperature.     

Variable Temperature Stress in the Nematode Caenorhabditis elegans (Maupas) and Its Implications for Sensitivity to an Additional Chemical Stressor

A wealth of studies has investigated how chemical sensitivity is affected by temperature, however, almost always under different constant rather than more realistic fluctuating regimes. Here we compared how the nematode Caenorhabditis elegans responds to copper at constant temperatures (8–24°C) and under fluctuation conditions of low (±4°C) and high (±8°C) amplitude (averages of 12, 16, 20°C and 16°C respectively). The DEBkiss model was used to interpret effects on energy budgets. Increasing constant temperature from 12–24°C reduced time to first egg, life-span and population growth rates consistent with temperature driven metabolic rate change. Responses at 8°C did not, however, accord with this pattern (including a deviation from the Temperature Size Rule), identifying a cold stress effect. High amplitude variation and low amplitude variation around a mean temperature of 12°C impacted reproduction and body size compared to nematodes kept at the matching average constant temperatures. Copper exposure affected reproduction, body size and life-span and consequently population growth. Sensitivity to copper (EC₅₀ values), was similar at intermediate temperatures (12, 16, 20°C) and higher at 24°C and especially the innately stressful 8°C condition. Temperature variation did not increase copper sensitivity. Indeed under variable conditions including time at the stressful 8°C condition, sensitivity was reduced. DEBkiss identified increased maintenance costs and increased assimilation as possible mechanisms for cold and higher copper concentration effects. Model analysis of combined variable temperature effects, however, demonstrated no additional joint stressor response. Hence, concerns that exposure to temperature fluctuations may sensitise species to co-stressor effects seem unfounded in this case.     

Functional Assessment of Cardiac Responses of Adult Zebrafish (Danio rerio) to Acute and Chronic Temperature Change Using High-Resolution Echocardiography

The zebrafish (Danio rerio) is an important organism as a model for understanding vertebrate cardiovascular development. However, little is known about adult ZF cardiac function and how contractile function changes to cope with fluctuations in ambient temperature. The goals of this study were to: 1) determine if high resolution echocardiography (HRE) in the presence of reduced cardiodepressant anesthetics could be used to accurately investigate the structural and functional properties of the ZF heart and 2) if the effect of ambient temperature changes both acutely and chronically could be determined non-invasively using HRE in vivo. Heart rate (HR) appears to be the critical factor in modifying cardiac output (CO) with ambient temperature fluctuation as it increases from 78 ± 5.9 bpm at 18°C to 162 ± 9.7 bpm at 28°C regardless of acclimation state (cold acclimated CA– 18°C; warm acclimated WA– 28°C). Stroke volume (SV) is highest when the ambient temperature matches the acclimation temperature, though this difference did not constitute a significant effect (CA 1.17 ± 0.15 μL at 18°C vs 1.06 ± 0.14 μl at 28°C; WA 1.10 ± 0.13 μL at 18°C vs 1.12 ± 0.12 μl at 28°C). The isovolumetric contraction time (IVCT) was significantly shorter in CA fish at 18°C. The CA group showed improved systolic function at 18°C in comparison to the WA group with significant increases in both ejection fraction and fractional shortening and decreases in IVCT. The decreased early peak (E) velocity and early peak velocity / atrial peak velocity (E/A) ratio in the CA group are likely associated with increased reliance on atrial contraction for ventricular filling.     

On the Temperature Behavior of Pulse Propagation and Relaxation in Worms,Nerves and Gels

The effect of temperature on pulse propagation in biological systems has been an important field of research. Environmental temperature not only affects a host of physiological processes e.g. in poikilotherms but also provides an experimental means to investigate the thermodynamic phenomenology of nerves and muscle. In the present work, the temperature dependence of blood vessel pulsation velocity and frequency was studied in the annelid Lumbriculus variegatus. The pulse velocity was found to vary linearily between 0°C and 30°C. In contrast, the pulse frequency increased non-linearly in the same temperature range. A heat block ultimately resulted in complete cessation of vessel pulsations at 37.2±2.7°C (lowest: 33°C, highest: 43°C). However, quick cooling of the animal led to restoration of regularly propagating pulses. This experimentally observed phenomenology of pulse propagation and frequency is interpreted without any assumptions about molecules in the excitable membrane (e.g. ion channels) or their temperature-dependent behaviour. By following Einstein’s approach to thermodynamics and diffusion, a relation between relaxation time τ and compressibility κ of the excitable medium is derived that can be tested experimentally (for κ_T ∼ κ_S). Without fitting parameters this theory predicts the temperature dependence of the limiting (i.e. highest) pulse frequency in good agreement with experimental data. The thermodynamic approach presented herein is neither limited to temperature nor to worms nor to living systems. It describes the coupling between pulse propagation and relaxation equally well in nerves and gels. The inherent consistency and universality of the concept underline its potential to explain the dependence of pulse propagation and relaxation on any thermodynamic observable.     

ON THE EQUILIBRATION OF GEOTROPIC AND PHOTOTROPIC EXCITATIONS IN THE RAT

The intensity of light required to just counterbalance geotropic orientation of young rats, with eyelids unopened, is so related to the angle of inclination (α) of the creeping plane that the ratio log I/log sin α is constant. This relationship, and the statistical variability of I as measured at each value of α, may be deduced from the known phototropic and the geotropic conduct as studied separately, and affords proof that in the compounding of the two kinds of excitation the rat is behaving as a machine.     

Phototropism and Local Adaptation in Phycomyces Sporangiophores

Phototropic responses to unilateral ultraviolet stimuli were studied to determine whether the response of one side of the cell is affected by the previous exposure of the opposite side to ultraviolet. It has been found that the direction of bending is not parallel to the stimulus direction, but is along a straight line rotated 17° clockwise from the stimulus direction. This deviation indicates that the photoreceptors may be in a state of continual clockwise rotation. If before the stimulus the cell is exposed briefly to ultraviolet and rotated through 90°, the response is not along the 17° line, but is deviated a greater or lesser amount, depending on whether the 90° rotation is clockwise or counterclockwise. This difference is evidence that the first ultraviolet exposure leaves a persistent patch of light-adapted receptors and the shaded part of the cell remains dark adapted. The phototropic stimulus straddles the edge between light- and dark-adapted regions, and the differing responses of the two regions affects the direction of phototropic bending. A phototropic mechanism is proposed which combines the features of local adaptation and photoreceptor rotation.     

ON THE TEMPERATURE CHARACTERISTICS FOR FREQUENCY OF BREATHING MOVEMENTS IN INBRED STRAINS OF MICE AND IN THEIR HYBRID OFFSPRING. I

Young mice of a selected line of the dilute brown strain of mice exhibit over the range 15–25°C. (body temperature) a relation of frequency of breathing movements to temperature such that when fitted by the Arrhenius equation the data give a value for the constant µ of 24,000± calories or, less frequently, 28,000±. Young mice of an inbred albino strain show over the range 15–20°C. a value of µ = 34,000±, or, less frequently, 14,000±, with a critical temperature at about 20°C. and a value of µ = 14,000± above 20°C. The F₁ hybrids of these two strains, and the backcross generations to either parent strain, exhibit only those four values of the temperature characteristic observed in the parent strains and none other. One may therefore speak of the inheritance of the value of the constant µ, but the inheritance shows in this instance no Mendelian behavior. Furthermore there appears to be inherited the occurrence (or absence) of a critical temperature at 20°C. These experiments indicate the "biological reality" of the temperature characteristics.     

Fahrenheit 101

Is there any convincing explanation for why mammals and birds maintain their body temperature close to 40°C? Subject Categories: Ecology, Metabolism,

Having recently become very interested in the way organisms balance heat production against “useful work”, I have stumbled into an old‐chestnut question in biology. That is, why do birds and mammals maintain their body temperature close to 40°C—at least during periods of normal circadian activity—regardless of their size or their local environment? This question comes into even sharper focus when realizing that the vast majority of organisms on our planet do not do anything like this, and still thrive at temperatures anywhere between below the freezing and above the boiling point of water. Warm‐blooded animals as a whole represent only a fraction of a percent of the total biomass on Earth. Most animals live at or very close to environmental temperature. Moreover, birds and mammals inhabit similar environments to all those other organisms, ranging from the cool depths of the oceans to the dramatic temperature fluctuations of the world''s deserts. The male emperor penguin (Aptenodytes forsteri) overwinters on the landward side of the Antarctic sea ice, remaining almost motionless for months, while incubating his egg at air temperatures some 70–80°C cooler than that of his own body, without even factoring in the additional chill of frequent gale‐force winds, and then goes off foraging in the comparatively warm waters at the ice edge and beyond, maintaining all the time his body temperature at the same 38–39°C. The only significant deviation from the 40°C rule is the special case of hibernation and torpor, although the extent and frequency of the associated body temperature decrease(s) vary greatly between species.Whenever I have posed this question to colleagues or students or just about anyone, I invariably get a similar answer: that this must be the optimal temperature for life, for the stability of proteins; for the functionality of enzymes; for just the right amount of membrane fluidity to facilitate cell–cell signaling, endocytosis, exocytosis, and charge separation; and for the highest fidelity of nucleic acid and protein synthesis. Even if these assertions are true—and I am not aware of compelling evidence that they are—this flies in the face of the fact that the vast bulk of non‐homeothermic organisms are not to be found in the very few environments on the planet that come close to the range of avian and mammalian body temperatures. Instead, life seems concentrated in the cool soil and oceans, and in great forests found in equatorial, temperate, and even sub‐polar climes alike. The most biologically productive zone of the world''s oceans is not even in the tropics, but at the Antarctic convergence, which is teeming with animal, plant, and bacterial life. Moreover, if 40°C were so favorable, wouldn''t homeothermy geared to maintaining that temperature have evolved countless times, in different organisms? Or, for that matter, wouldn''t the proteins and membranes of birds and mammals have evolved so as to function better at temperatures closer to the global average of around 10–15°C, instead of wasting all that energy to stay warm? After all, if the Antarctic sea urchin (Sterechinus neumayerii) has adapted over a few tens of millions of years to live and develop perfectly well at −1.5°C (Foo et al, 2016), just more slowly than its close relatives in temperate or tropical waters, what''s stopping us from having turned down the heat by the same amount?I anticipate that you are now expecting me to reveal a brilliant idea to explain everything. But all I have to offer are new meanderings and wrong turnings. The first is the idea that, like the traditional explanation for our cellular and blood salinity being close to that of the ancient ocean, maybe that ancient ocean was stable at 40°C for most of evolutionary time. Except that it was not. It was closer to 80°C throughout at least the first half of our planet''s history, when the major cellular forms evolved (Knauth, 2005), and after that, it cooled down to below the magic 40°C and remained there ever since, albeit with large fluctuations. During the period when warm‐blooded creatures are believed to have arisen, the oceans never rose to 40°C, and in any case, this evolutionary step is generally assumed to have occurred on land, not in water.Do our own observations that mitochondria are 10–12°C warmer than the cells in which they reside (Chrétien et al, 2018) have any bearing on the question? Is this again some kind of happy medium, whereby the maximum efficiency of oxidative phosphorylation dictates a certain heat output that naturally maintains the cell’s temperature at around 40°C? But if this were the case, other eukaryotes that did not maintain any kind of internal thermoregulation at the whole‐organism level would also tend to be at 40°C, with their mitochondria at 50°C. Yet mitochondria in Drosophila cells are again about 10°C warmer than their surroundings, but at much cooler ambient temperatures (M. Terzioglu & H. T. Jacobs, unpublished observations). And prolonged exposure to 40°C represents a lethal heat shock for wild‐type Drosophila (Stefanou & Alahiotis 1982). Poikilotherms simply lose excess heat to the environment, whereas homeotherms must use specific mechanisms both to generate and to retain, additional heat when needed, and radiate excess heat to the outside, so as to maintain a constant internal temperature.Is there some other defining feature of mammalian and avian biology that might default body temperature to the observed constant? After much reflection, I cannot think of one. But perhaps it is possible to construe an argument in the opposite direction that having evolved mechanisms to maintain a constant body temperature, birds and mammals have, as argued elsewhere (Grigg et al, 2004), been able to colonize extremely diverse habitats, remain active at night, and perhaps resist mass extinction events driven by climate change a bit better than other taxa. But this did not help the dinosaurs. And it does not explain why 40°C is any better than 80 or 20°C, or why it is so evolutionarily stable, in birds of paradise as in penguins, or kangaroos as in polar bears.Perhaps one can cobble some argument together by combining the adaptive range and mitochondrial arguments; plus the fact that it is probably easier to envisage single mutations that can shift the balance between metabolic heat production and useful work, to maintain 40°C, as opposed to the many mutations required to re‐optimize biological processes for a different temperature. But I am not very convinced. Evolution normally mirrors environmental change, rather than resists it.If an intelligent insect were writing this column, they would no doubt herald the virtues of the arthropod lifestyle in being able to go with the climactic flow and not waste so much energy keeping warm or cool like all those primitive furry and feathered creatures, yearning for their balmy but non‐existent Eden. Maybe some reader out there will come up with a cute idea that will prove experimentally testable and eventually seem self‐evident, yet has escaped me and all others who have pondered this question. But I am now going out to frolic in the snow. Over to you.     

THE RATE OF OXYGEN UTILIZATION BY YEAST AS RELATED TO TEMPERATURE

Suspensions of the yeast Saccharomyces cerevisiae gave reproducible rates of O₂ uptake over a period of 6 months. The relation of rate of consumption of O₂ to temperature was tested over a wide range of temperatures, and the constant in the formulation of the relationship is found to be reproducible. The values of this constant (µ) have been obtained for five separate series of experiments by three methods of estimation. The variability of µ has the following magnitudes: the average deviation of a single determination expressed as per cent of the mean is ±2 per cent in the range 30–15°, and ±0.8 per cent in the range 15–3°C. This constancy of metabolic activity measured as a function of temperature can then be utilized for more precise investigations of processes controlling the velocity of oxidations of substrates, and of respiratory systems controlled by intracellular respiratory pigments. The data plotted according to the Arrhemus equation give average values of the constant µ as follows: for the range 35–30°, µ = 8,290; 30–15°, µ = 12,440 ±290; 15–3°, µ = 19,530 ±154. The critical temperatures are at 29.0° and 15.7°C. A close similarity exists between these temperature characteristics (µ) and values in the series usually obtained for respiratory activities in other organisms. This fact supports the view that a common system of processes controls the velocities of physiological activities in yeast and in other organisms.     

STIMULATION OF FUNDULUS BY OXALIC AND MALONIC ACIDS AND BREATHING RHYTHM AS FUNCTIONS OF TEMPERATURE

1. Chemical stimulation as a function of temperature was studied by using oxalic acid in fresh and salt water and malonic acid in salt water as stimulating agents on Fundulus. According to the Arrhenius equation the following µ values were obtained for the various acid solutions between 0 and 29°C.: for 0.002N oxalic in fresh water—15,800; 33,000; for 0.0008N oxalic in fresh water—15,800; 33,000; 48,000; for 0.002N oxalic in salt water—19,400; 24,100; 56,500; for 0.004N and 0.002N malonic in salt water—20,600; 65,000. At a critical temperature there is a sharp transition from one thermal increment to another. 2. The chemical processes controlling stimulation do not change with concentration, for different normalities of a single acid yield the same µ values. Distinctly different temperature characteristics were obtained for stimulation by oxalic in salt and fresh water. Likewise stimulation by oxalic and malonic in salt water yielded very different increments. This temperature study indicates that the controlling chemical reactions determining rate of response are different for the same acid in two different environments, or for two dibasic acids in the same environment. Other work indicates, however, that the fundamental stimulation system is the same for all the adds in both environments. Chemical rather than physical processes limit the rate of response since all the values are above 15,000. Stimulation depends upon a series of interrelated chemical reactions, each with its own temperature characteristic. Under varying conditions (e.g. change of temperature, environment, or acid) different chemical reactions may become the slowest or controlling process which determines the rate of response. 3. The variation of response, as measured by the probable error of the mean response time of the fish, is the same function of temperature as reaction time itself. Hence variability is not independent of reaction time and is controlled by the same catenary series of events which determine rate of response to stimulation. 4. Breathing rhythm of Fundulus as related to temperature was studied in both salt and fresh water. In salt water the temperature characteristic is 8,400 while in fresh water it is 16,400 below 9.5°C., and 11,300 above this critical temperature. These µ values are typical of those which have been reported by other workers for respiratory and oxidative biological phenomena. A change in thermal increment with an alteration in environment indicates that different chemical reactions with characteristic velocity constants are controlling the breathing rhythm in salt and fresh water.     

CRITICAL THERMAL INCREMENT FOR THE MOVEMENT OF OSCILLATORIA

In a species of Oscillatoria exhibiting movement of type suitable for exact measurement the velocity of linear translatory motion is found to be controlled by the temperature (6 – 36°C.) in accordance with Arrhenius'' equation for irreversible reactions. The value of the critical increment (µ) is 9,240. The extreme variates in series of measurements at different temperatures yield the same value of µ. The velocity of movement is therefore regarded as determined by the velocity of an underlying chemical process, controlled by the temperature and by the amount of a substance (? catalyst) whose effective quantity at any moment varies within definite limits in different filaments of the alga. On the basis of its temperature characteristic the locomotion of Oscillatoria is compared with certain other processes for which this constant is calculated.