given for one animal in curve A of figure 5. It is entirely typical of the other experiments. Curve A of figure 6 expresses similarly the average results of an experiment on the relation of temperature to the velocity of pulsation. This may best be shown as the time required for a contraction wave to pass over a given distance along the heart. The two curves resemble the numerous figures that have already been drawn to show the relation of temperature to various life processes (Kanitz, '15). Although there has been much controversy about the exact shape of such curves in general, the matter is far from settled. Snyder ('13), among others, has consistently supported the idea that they are exponential in character, whereas Krogh ('14), for example, has interpreted similar results as linear functions of the temperature. A minor source of confusion in this connection is the difference in 1 the methods of recording data. It will be remembered that y= x repre sents the equation for an hyperbola referred to its asymptotes as axes, and that y=x is the equation of a straight line. Consequently, much depends on whether the experimental value itself or its reciprocal is used in plotting the results. Figure 5 represents just such a situation. Curves A and B have the same abscissas, whereas the ordinates of one are the reciprocals of those of the other. In the one case the curves resemble an hyperbola; in the other, a straight line. Only a few of the discrepancies (cf. Krogh, '14, p. 170), however, are to be explained on the basis of this confusion. In Ascidia, for example, two phases of the activity of the same organ show the two types. of results illustrative of the effect of temperature. Curves B of figure 5 show that the pulse rate is clearly a linear function of the temperature. Its temperature coefficient is therefore constant for the complete range of its normal activity. The velocity of the pulsation wave, however, is an exponential function of the temperature (B, fig. 6), and its temperature coefficient varies from 2.1 to 2.9. In spite of the heated controversy (Snyder, '13, p. 77, footnote), it is difficult to see wherein either result is possessed of any great significance. The earlier investigators were much impressed by the resemblance between the temperature coefficient of protoplasmic activity and of chemical reactions. On this similarity was based the conclusion, for example, that the underlying process of the heart beat is a single chemical reaction (Harvey, '11). It must, however, be clear at present that this is much too simple an explanation. Any protoplasmic movement is composed of several chemical and physical reactions, which may differ in direction, velocity and intensity (cf. especially, Pütter, '14). A few of the more obvious physiologic factors which are concerned in the heart beat of Ascidia atra are: the origin of the internal stimulus, its propagation through the cell, the refractory period of the muscle and the degree of its irritability. Each of these is undoubtedly conditioned by several reactions which result in an interplay of several kinds of energy. A change of temperature has an individual effect on these numberless reactions, and it is their resultant which is expressed by the relation of the temperature to the frequency of the pulsation. The remarkable thing, to my mind, is not whether the relation between temperature and pulse rate is linear or exponential, but that there exists any definite relation at all. The real significance of temperature effects will not become clear from a superficial comparison with simple chemical reactions. Their interpretation will come only after an analysis of the principal reactions concerned in protoplasmic activity, much as the understanding of the timbre of a musical sound is the result of its resolution into the tones and overtones combined in its production. IV. SUMMARY 1. The blood of Ascidia atra is colorless and transparent. It flows through the body under an appreciable pressure. 2. The blood plasma is isotonic with seawater. 3. The blood has an acid reaction; the acidity is resident in the green corpuscles and not in the plasma. 4. There are at least two kinds of cells in the blood: pigmented and unpigmented. Of the pigmented cells, the green are distributed all over the body; the orange are localized in the branchial sac; and the blue are found in the regions of the viscera, etc. Some of the unpigmented cells are ameboid; others are not. 5. In the green cells, the pigment is a compound containing vanadium, probably in a stage of oxidation corresponding to V2O3. It is not a respiratory pigment but is most likely of value as a catalytic agent. 6. The coagulation of the blood depends on the agglutination of its cells. Clotting often occurs within the intact blood system as a result of vigorous external stimulation. 7. The heart of Ascidia atra is long and has a node which divides it unequally. The presence of the node may be demonstrated physiologically as well as anatomically. 8. A pericardial body is present. 9. In most of the animals a pulsation series shows about twice as many advisceral beats as abvisceral beats. 10. The pulse rate decreases as the size of the animal increases. It is greater in the advisceral phase than in the abvisceral phase. 11. The velocity of the contraction wave is greater in the advisceral direction than in the abvisceral direction. 12. The greater activity of the heart during the abvisceral phase of a pulsation cycle indicates that, in spite of the periodic reversal of direction, there is a resultant circulation of the blood in the advisceral direction. 13. These facts are incompatible with the "back pressure" explanation of the periodic reversal of the heart beat. They are, however, in harmony with the idea that the reversal is due to the alternating dominance as pacemakers of the two ends of the heart. 14. The presence of a central beat, the suppression of the abvisceral beat and the magnitude of the velocity of the pulsation wave indicate that the heart beat is myogenic, and that the contraction wave passes along the muscular elements across the heart. 15. The pulsation rate is a linear function of the temperature, whereas the velocity of the pulsation wave is an exponential function of the temperature. Neither relation is shown to be of real significance in view of the complexity of reactions involved in the heart beat. BIBLIOGRAPHY ALEXANDROWICZ, J. S. '13 Zeitschr. allg. Physiol., xiv, 358. ALSBERG, C. L., AND M. W. CLARK. '14 Journ. Biol. Chem., xix, 503. BANCROFT, F. W., AND C. O. ESTERLY. '03 Univ. Calif. Publ. Zoöl., i, 105. BURROWS, M. T. '12 Sci., N. S., xxxvi, 90. '15 Bodily changes in pain, hunger, fear and rage. New DREW, G. H. '10 FERNANDEZ, M. '16 This Journal, xii, 67. Journ. Exper. Zool., xx, 297. Arch. Zool. Expér., Sér. 2, ix, 13. R. A. THACKER. '14 Journ. Physiol., xlvii, 493. Quart. Jour. Micr. Sci., liv, 605. '06 Jena. Zeitschr., xli, 1. FRIEDLÄNDER, B. '88 Biol. Centralbl., viii, 363. FÜRTH, O. VON '03 Jena. GARREY, W. E. '11 Vergleichende chemische Physiologie der niederen Tiere. This Journal, xxviii, 330. GAVER, F., VAN AND P. STEPHEN. '07 C. R. Soc. Biol., lxii, 554. HARLESS, E. '47 Arch. Anat. Physiol., 148. HARVEY, E. N. '11 '18 a '18 b HELLER, C. '75 HENZE, M. '11 Carnegie Instn. Publ., no. 132, 27. '24 Ann. Sci. Nat., Zool., iii, 78. Journ. Exper. Zoöl., xx, 429. Journ. Exper. Zoöl., xxv, 261. Denk. Akad. Wiss. Wien. Math.-Nat. Classe, xxxiv, Abt. 2, 1. '12 Zeitschr. physiol. Chem., lxxix, 215. '13 Zeitschr. physiol. Chem., lxxxvi, 340. HERDMAN, W. A. '04 Cambridge Nat. Hist., vii, 33. HÖBER, R. '14 Physikalische Chemie der Zelle und der Gewebe, Leipzig und Berlin. JENKINS, O. P., AND A. J. CARLSON. '04 Journ. Comp. Neurol., xiii, 259. KROGH, A. '14 Zeitschr. allg. Physiol., xvi, 162. KRUKENBERG, C. F. W. '80 a Vergleichend-Physiol. Studien, I. Reihe, Abt. iii, 66. '80 b Vergl.-Physiol. Studien, I. Reihe, Abt. iii, 151. LAHILLE, F. '90 Contributions a l'étude anatomique et taxonomique des Tuniciers. Thèse, Paris. LOEB, J. 02 Comparative physiology of the brain and comparative psychology, New York. LOEB, L. '10 Biochem. Zeitschr., xxiv, 478. NICOLAI, G. F. '08 Arch. Anat. Physiol., Physiol. Abt., Suppl. Bd., Jahrg. 1908, 87. PÜTTER, A. '07 Zeitschr. allg. Physiol., vii, 283. '14 Zeitschr. allg. Physiol., xvi, 574. RITTER, W. E. '93 Proc. Calif. Acad. Sci., Ser. 2, iv, 37. ROULE, L. '84 Reichs, iii, Jena. Zeitschr., xxxv, 221. Tunicata. Bronn's Klassen und Ordnungen des Tier(suppl.), Abt. 1, 1. SNYDER, C. D. '13 Zeitschr. allg. Physiol., xv, 72. TODARO, F. '85 Atti R. Accad. Lincei, ser. 4, Mem. i, 641. EVIDENCE FOR THE ENZYMATIC BASIS OF HEART-BEAT1 MARY MITCHELL MOORE From the Physiological Laboratory of Rutgers College, New Brunswick, New Jersey Received for publication December 6, 1917 Among the many investigators who studied the effect of temperature on the heart-beat, Cyon (1) did the most conclusive of early work. He studied the effect of changes of temperature on the number, duration and strength of the beats of the excised frog heart. He found that the rate increased regularly with the temperature until the number of beats reached a maximum. After reaching this point the rate became irregular and slowed rapidly so that the heart came to rest only a few degrees above the maximum, between 30° and 40°. These observations were extended and confirmed for the mammalian heart by Newell Martin (2) and by Langendorff (3). G. N. Stewart (4) found that extreme high temperatures cause first an increase in rate to a maximum and later a decrease followed by standstill in the hearts of the frog, toad and turtle. The same was found to be true of the terrapin heart by E. G. Martin (5). The problem took on a new aspect with the application of the law of van't Hoff and Arrhenius to biological reactions. This law applies to chemical reactions and states that for every increase of ten degrees in temperature the rate of reaction is doubled or trebled. A great number of investigators have established the fact that metabolic processes are influenced by heat in the same direction and degree as chemical reactions, and they have shown that the law holds for medium. temperatures (10° to 27°). The conclusion arrived at is that life activities are at bottom chemical. The question at issue is, Does the law hold for higher temperatures, and in case of deviation, what are the modifying factors? The heartbeat of crustacea (6), of cold-blooded (7) and warm-blooded vertebrates (8) has been shown to obey this law within the medium range. If the law holds for higher temperatures, the heart ought to beat with 1 Submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Rutgers College. |