196 CIRCULATION. 



elastic tube with the registering apparatus. All the tubes 

 are provided with stop-cocks, so that each initial bag may be 

 made to communicate with its lever at will. When the oper- 

 ation is concluded, and the sound firmly secured in place by 

 a ligature around the vein, the animal experiences no incon- 

 venience, is able to walk about, eat, &c., and there is every 

 evidence that the circulation is not interfered with. The 

 cylinders which carry the paper destined to receive the traces 

 are arranged to move by clock-work at a given rate. The 

 paper may also be ruled in lines, the distances between which 

 represent certain fractions of a second. 



Fig. 2, taken from the work of Marey, represents the 

 apparatus reduced to one-sixth of its actual size. Two of 

 the levers are connected with the double sound for the right 

 auricle and ventricle, and one is connected with the bag des- 

 tined to receive the impulse of the heart. 



In an experiment upon a horse, every thing being care- 

 fully arranged in the way indicated, the clock-work was set 

 in motion, and the movements of the three levers produced 

 traces upon the paper which were interpreted as follows : 



1. The paper was ruled so that each division represented 

 one-tenth of a second. The traces formed by the three levers 

 indicated four revolutions of the heart. The first revolution 

 occupied 1^ sec., the second 1-^- sec., the third 1 T V sec., and 

 the fourth 1 sec. 



2. The auricular systole, as marked by the first lever, 

 immediately preceded the ventricular systole, and occupied 

 about two-tenths of a second. The elevation of the lever 

 indicated that it was much more feeble than the ventricular 

 systole, and sudden in its character ; the contraction, when 

 it had arrived at the maximum, being immediately fol- 

 lowed by relaxation. 



3. The ventricular systole, as marked by the second lever, 

 followed immediately the auricular systole, and occupied 

 about four-tenths of a second. The almost vertical direc- 

 tion of the trace, and the degree of elevation, showed that it 



