44 CIRCULATION OF THE BLOOD. 



The great points in the succession of movements are readily observed in the hearts 

 of cold-blooded animals, in which the pulsations are very slow. In examining the heart 

 of the frog, turtle, or alligator, the alternations of repose and activity are very strongly 

 marked. During the intervals of contraction, the whole heart is flaccid, and the ventricle 

 is comparatively pale ; we then see the auricles slowly filling with blood ; when they 

 have become fully distended, they contract and fill the ventricle, which, 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. 

 This operation may occupy from ten to twenty seconds, giving an abundance of time for 

 observation. 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 we have just 

 mentioned are followed with the utmost difficulty. In spite of this rapidity of action, it 

 can be seen that a rapid contraction of the auricles precedes the ventricular systole, and 

 that the latter is synchronous with the impulse. 



Various estimates have been made of the relative time occupied by the auricular and 

 ventricular contractions; and the question has been at last definitely settled by the 

 observations of Marey, who has constructed very ingenious and delicate instruments for 

 registering the form and frequency of the pulse. He devised a series of most interesting 

 experiments, in which he was enabled to register simultaneously the pulsations of the 

 different divisions of the heart, and has succeeded in establishing a definite relation be- 

 tween the contractions of the auricles and ventricles. The method of Marey enables 

 us to determine, to a small fraction of a second, the duration of the contraction of each 

 of the divisions of the heart. 



The method of transmitting the movement from the heart to a registering apparatus 

 is very simple. The apparatus consists of two little elastic bags connected together by 

 an elastic tube, the whole closed and filled with air. A pressure, like the pressure of 

 the fingers, upon one of these bags produces, of course, an instantaneous and correspond- 

 ing dilatation of the other. If we suppose one of these bags to be introduced into one 

 of the cavities of the heart, and the other placed under a small lever arranged on a pivot 

 so as to be sensible to the slightest impression, it is evident that any compression of the 

 bag in the heart would produce a corresponding change in volume in the other bag, 

 which would be indicated by a movement of the lever. Marey arranged the lever with 

 its short arm on the elastic bag, and the long arm, provided with a pen, moving against 

 a roll of paper, which passes along at a uniform rate. When the lever is at rest with the 

 paper set in motion, the pen will make a horizontal mark ; but when the lever ascends 

 and descends, a corresponding trace will be made, and the duration of any movement 

 can readily be estimated by calculating the rapidity of the motion of the paper. The bag 

 which receives the impression is called by Marey the initial bag, and the other, which is 

 connected with the lever, is called the terminal bag. The former may be modified in 

 form with reference to the situation in which it is to be placed. 



The experiments of M. 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 jugular vein, an 

 operation which may be performed with certainty and ease. 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 corresponding 

 movements of the levers, which may be registered simultaneously. 



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



