CIRCULATION. 405 



regularly recurring changes of size in the auricles, the ventricles, and the 

 arteries. These changes of size are accompanied by corresponding changes 

 in the form and position of the heart, which are both interesting in them- 

 selves and important in relation to the diagnosis of disease. The basis 

 of their study consists in opening the chest and pericardium of an animal, 

 and seeing, touching, and otherwise investigating the beating heart. The 

 changes in the beating heart, moreover, underlie the production of the 

 so-called cardiac impulse, or apex-beat, which is of interest in physical 

 diagnosis. 



Observation of the Heart and Vessels in the Open Chest. The beat- 

 ing heart may be exposed for observation in a mammal by laying it upon it.s 

 back, performing tracheotomy, and completely dividing the sternum in the 

 median line, beginning at the ensiform cartilage. Artificial respiration is next 

 established, a tube having been tied into the trachea before the chest was 

 opened. The two sides of the chest are now drawn asunder and the pericar- 

 dium is laid open to expose the heart. 



If, in any mammal, the ventricles be lightly taken between the thumb and 

 forefinger, the moment of their systole is revealed by the sudden hardening of 

 the heart produced by it, as the muscular fibres contract and press with force 

 upon the liquid within. On the other hand, the ventricular diastole is marked 

 by such flaccidity of the muscular fibres that very light pressure indents the 

 surface, and causes the finger to sink into it, in spite of care being taken to 

 prevent this. Commonly, therefore, at the systole the thumb and finger are 

 palpably and visibly forced apart, no matter where applied, in spite of the fact 

 that the volume of the ventricles is diminishing. This sinking of the finger 

 or of an instrument into the relaxed wall of the heart has given rise to many 

 errors of observation regarding changes during the beat. The time when the 

 ventricles are hardened beneath the finger coincides with the up-stroke of the 

 arterial pulse near the heart, and, as shown by Harvey, 1 with the time when 

 an intermittent jet of blood springs from a wound of either ventricle. The 

 hardening is proven thus to mark the systole of the ventricles. Those changes 

 of size, form, and position of the exposed heart which accompany the harden- 

 ing of the ventricles beneath the finger are therefore the changes of the ven- 

 tricular systole ; and the converse changes are those of the ventricular diastole. 

 To interpret all the changes correctly by the eye alone, without the aid of the 

 finger or of the jet of blood, is a task of surpassing difficulty in a rapidly beat- 

 ing heart, as was eloquently set forth by Harvey. 2 



Changes of Size and Form in the Beating- Ventricles. In a mam- 

 mal, lying upon its back, with the heart exposed, the ventricles evidently 

 become smaller during their systole. Their girth is everywhere diminished 

 and their length also, the latter much less than the former ; indeed the dimi- 

 nution in length is a disputed point. Not merely a change of size, but a 



1 Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus, 1628, p. 23; Willis' trans- 

 lation, Bowie's edition, 1889, p. 23. 



3 Op. tit., 1628, p. 20; Willis' translation, Bowie's edition, p. 20. 



