CIRCULATION. 397 



The Pulse-volume. The central fact of the circulation of the blood is the 

 injection, at intervals, by each ventricle, against a strong resistance, of a charge 

 o blood into its artery, which charge the ventricle has just received out of its 

 veins through its auricle. This quantity must be exactly the same for the 

 two ventricles under normal conditions, or the circulation would soon come to 

 an end by the accumulation of the blood in either the pulmonary or the sys- 

 temic vessels. The blood ejected from each ventricle during the systole 

 must also be equal in volume to the blood which enters each set of capillaries, 

 the pulmonary or systemic, during that systole and the succeeding diastole of 

 the ventricles, provided the circulation be proceeding uniformly. The quantity 

 just referred to is called the "contraction volume" or " pulse- volume " of the 

 heart. Were it always the same, and could we measure it, we should possess 

 the key to the quantitative study of the circulation. 



The pulse-volume may vary in the same heart at different times, as is easily 

 shown by opening the chest, causing the conditions of the circulation to change, 

 and noting that under certain conditions the heart during each beat varies 

 in size more than before. This variation of volume is easily possible because 

 the walls of the heart are of muscle, soft and distensible when relaxed. It is 

 probable that at no systole is the ventricle quite emptied ; that most of its 

 cavity may become obliterated by the coming together of its walls, but that a 

 space remains, just below the valves and above the papillary muscles, which is 

 not cleared of blood 1 : It is also probable that not only the blood which is 

 ejected at the systole may vary in amount, but also the residual blood which 

 remains in the ventricle at the end of the systole. 1 It is therefore clear that 

 it is useless to attempt the measurement of the pulse-volume by measuring 

 the fluid needed to fill the ventricle, even if the heart be freshly excised from 

 the living body and injected under the normal blood-pressure. Rough approx- 

 imations' to this measurement may, however, be attempted in at least two 

 ways : 



In the first place, a modification of the stromuhr has been applied suc- 

 cessfully to the aorta of the rabbit, between the origins of the coronary arteries 

 and of the innominate. This operation requires that the auricles be clamped 

 temporarily so as to stop the flow of blood into the ventricles, and to permit 

 the aorta in its turn to be clamped and divided between the clamp and the 

 ventricle, without serious bleeding. After the circulation has been re-estab- 

 lished, the volume of the blood which passes through the instrument during 

 the experiment, divided by the number of the heart-beats during the same 

 period, gives the pulse-volume. The average result obtained, for the rabbit, 



1 F. Hesse: "Beitrage zur Mechanik der Herzbewegung," Archivfiir Anatomie und Physiolo- 

 gic (anatomische Abtheilung), 1880, p. 328. C. Sandborg und W. Miiller : " Studien iiber den 

 Mechanismus des Herzens," Pfluger's Archivfiir die gesammte Physiologic, 1880, xxii. p. 408. C. S. 

 Roy and J. G. Adami : " Contributions to the Physiology and Pathology of the Mammalian 

 Heart," Proceedings of the Royal Society of London, 1891-92, i. p. 435. J. E. Johansson und R. 

 Tigerstedt : " Ueber die gegenseitigen Beziehungen des Herzens und der Gefasse ;" " Ueber die 

 Herzthatigkeit bei verschieden grossem Wiederstand in den Gefassen," Skandinavisches Archiv 

 fur Physiologic, 1891, ii. p. 409. 



