194 CIRCULATION. 



sure of the fingers, upon one of these bags produces, of course, 

 an instantaneous and corresponding 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 le- 

 ver, so arranged on a pivot 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, which would be indicated by a movement of 

 the lever. M. Marey has 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 and 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 es- 

 timated 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 rela- 

 tions 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 is performed 

 with certainty and ease. 1 This sound is provided with two 

 initial bags, one of which is lodged in the right auricle, while 



1 Catheterization of the cavities of the heart, especially upon the right side, is 

 an operation familiar to physiologists. With a double canula, such as is described 

 by Marey (p. 61), of the requisite dimensions and with the proper curves, it must 

 be easy to lodge the bags respectively in the auricle and ventricle ; especially in 

 an animal of large size like the horse. A tube is easily introduced into the right 

 side of the heart, in the dog, through the external jugular. M. Marey gives full 

 details of every step of the operation, and there can be no doubt of the facility and 

 accuracy with which it may be performed. 



