THERMAL INCREMENTS FOR PULSATION-FREQUENCY IN "ACCESSORY HEARTS" OF NOTONECTA

The frequencies of pulsation of the "accessory hearts" in the isolated swimming-legs of Notonecta were studied in relation to temperature, with the idea that in such organs central nervous control is impossible, and that in an isolated system irreversibly proceeding toward death it might be expected that further evidence would be found regarding the supposed specific significance of critical thermal increments. A number of values of µ are found, commonly 8,200; 16,200; or 32,200; less frequently 11,400; 19,800; and 24,500. These values are definitely contrasted with that (12,300) typical for heart beat frequencies in arthropods. They exhibit interrelationships of the sorts already found in other cases. There occur also sharp irreversible changes in frequency of pulsation, which may or may not be accompanied by change of increment. The net result is held to be confirmatory of the interpretation of thermal relations proposed in earlier papers

ON THE MODIFICATION OF TEMPERATURE CHARACTERISTICS

In December and January the frequency of heart beat in Limax exhibits µ = 11,500 ± 250. The ingestion of a small volume of sugar solution results in temporary change of µ to 16,200 ± 320, which accords quantitatively with the value obtained from these slugs in spring. This effect of the sugar is reversible, but lasts longer than the abolition of negative phototropism which the sugar also produces. Other instances are given in which the value of the temperature characteristics for vital processes have been changed experimentally. The new values which appear have already been obtained in connection with homologous activities. These results confirm the view that the critical thermal increments serve to characterize recognizably different governing reactions in living matter, and indicate a basis for specific experimental control

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

TEMPERATURE AND FREQUENCY OF CARDIAC CONTRACTIONS IN EMBRYOS OF LIMULUS

Temperature characteristics for frequency of myogenic heart beat in Limulus embryos, before the onset of nervous control of the heart, were found to be 11,500; 16,400; 20,000; 25,500. The two first values are the best established. The different values pertain to the hearts of different individuals outwardly similar, and to the hearts of single embryos in different parts of the temperature range. These values differ from that known in connection with the control of the heart beat through the cardiac ganglion. The occurrence of critical temperatures, also, is not the same in all embryos. These facts are employed in a discussion of temperature relations in pulsating explants of chick myocardium

THE MEASUREMENT OF GALVANOTROPIC EXCITATION

The expression of galvanotropic excitation in energy units is obtained by the measurement of the current densities required to balance phototropic excitation (or reciprocally). With the triclad Leptoplana preliminary measurements show that the current is proportional to the logarithm of the light intensity

TEMPERATURE CHARACTERISTIC FOR HEART BEAT FREQUENCY IN LIMAX

The temperature characteristic for the frequency of the heart beat in quiescent Limax maximus is µ = 16,300 calories. This value agrees well with that obtained for certain neurogenic activities of the parietal musculature of this gastropod

CRITICAL THERMAL INCREMENTS FOR RHYTHMIC RESPIRATORY MOVEMENTS OF INSECTS

The rhythm of abdominal respiratory movements in various insects, aquatic and terrestrial, is shown to possess critical increments 11,500± or 16,500± calories (Libellula, Dixippus, Anax). These are characteristic of processes involved in respiration, and definitely differ from the increment 12,200 calories which is found in a number of instances of (non-respiratory) rhythmic neuromuscular activities of insects and other arthropods. With grasshoppers (Melanoplus), normal or freshly decapitated, the critical increment is 7,900, again a value encountered in connection with some phenomena of gaseous exchange and agreeing well with the value obtained for CO2 output in Melanoplus. It is shown that by decapitation the temperature characteristic for abdominal rhythm, in Melanoplus, is changed to 16,500, then to 11,300—depending upon the time since decapitation; intermediate values do not appear. The frequency of the respiratory movements seems to be controlled by a metabolically distinct group of neurones. The bearing of these results upon the theory of functional analysis by means of temperature characteristics is discussed, and it is pointed out that a definite standpoint becomes available from which to attempt the specific control of vital processes

GEOTROPIC ORIENTATION IN ARTHROPODS : II. TETRAOPES.

The creeping of the beetle Tetraopes tetraopthalmus during negatively geotropic orientation shows the angles of orientation (θ) on a surface inclined at α° to the horizontal to be proportional to sin α. The direction of orientation easily suffers temporary reversal to positive as result of handling. Mechanical stability during upward progression should be just possible when K1 cot α = K2 sin θ + K3 cos θ, the weight of the body being supported on the tripod formed by the legs on either side and by the posterior tip of the abdomen. Lack of this stability produces tensions on the legs through (1) the bilaterally distributed pull of the body mass on the legs, and (2) the torque on the legs due to the weight of the abdomen. The downward gravitational displacement of the tip of the abdomen causes K2 and K3 in the preceding formula to be functions of α. These relations have been tested in detail by shifting the location of the center of gravity, by attaching additional masses anteriorly and posteriorly, and by decreasing the total load through amputation of the abdomen; the latter operation changes the conditions for stability. Different formulæ are thus obtained (cf. earlier papers) for the orientation of animals in which the mechanics of progression and the method of support of the body weight on an inclined surface are not the same. This demonstrates in a direct way that the respective empirical equations cannot be regarded as accidents. The results are in essence the same as that already obtained with young mammals. The diversity of equations required for the physically unlike cases merely strengthens the conception of geotropic orientation as limited by the tensions applied to the musculature of the body (caterpillars, slugs) or of appendages (beetles, and certain other forms) when the body is supported upon an inclined surface, since equations respectively pertaining to the several instances, and satisfactorily describing the observations, are deduced on this basis

GEOTROPIC ORIENTATION IN ARTHROPODS : I. MALACOSOMA LARVÆ.

The geotropic orientation of caterpillars of Malacosoma americana during progression upon a surface inclined at angle α to the horizontal is such that the path makes an average angle θ upward on the plane, of a magnitude proportional to log sin α. More precisely, the product (sin α) (sin θ) is constant. This is traced to the fluctuation of the pull of the head region upon the lateral musculature of the upper side during the side to side swinging implicated in progression