MOVEMENTS OF THE HEART. 41 



in these animals is single; the ventricle immediately contracts, its action 

 following upon the contraction of the auricles as if it were propagated from 

 them. When the heart is filled with blood, it has. a dark-red color, which 

 contrasts strongly with its appearance after the systole. These phenomena 

 may occupy ten to twenty seconds, giving an abundance of time for ob- 

 servation. The case is different, however, with the warm-blooded animals, 

 in which the anatomy of the heart is nearly the same as in man. Here a 

 normal revolution may occupy less than a second ; and it is evident that the 

 varied phenomena just mentioned are followed with more difficulty. In spite 

 of this rapidity of action, it can be seen that a rapid contraction of the auri- 

 cles precedes the ventricular systole, and that the latter is synchronous with 

 the cardiac impulse. 



The experiments of Marey, with reference to the relations between the 

 systole of the auricles, the systole of the ventricles and the impulse of the 

 heart, were performed upon horses, in the following way : 



A sound is introduced into the right side of the heart through the jugu- 

 lar vein. This sound is provided with two initial bags, one of which is 

 lodged in the right auricle, while the other passes into the ventricle. The 

 bags are connected with distinct tubes which pass one within the other and 

 are connected by elastic tubing with the registering apparatus. At each sys- 

 tole of the heart, the bags in its cavities are compressed and produce corre- 

 sponding movements of the levers, which may be registered simultaneously. 



FIG. Zl.Cuntioyrufjh (Chauveau ami Marey). 



" The instrument is composed of two principal elements : A E, the registering apparatus, and A S, the 

 sphygmographic apparatus, that is to say, which receives, transmits, and amplifies the movements 

 which are to be studied." The compression exerted upon the bag c, which is placed over the apex 

 of the heart, between the intercostal muscles, is conducted by the tube t c, which is filled with air. to 

 the first lever. The compression exerted upon the bags o and v, in the double sound, is conducted 

 by the tubes t o and t v to the two remaining levers. The movements of the levers are registered 

 simultaneously by the cylinder A E. 



To register the impulse of the heart, an incision is made through the skin 

 and the external intercostal muscle over the point where the apex-beat is felt. 



