232 CIRCULATION OF THE BLOOD. 



made by any artificial means. Just as, when the heart con- 

 tracts, it compresses its contents most energetically at the 

 outset, while its force rapidly diminishes towards the end of 

 the systole, so here the most rapid movement of the column is 

 at the first moment after the depression of the lever. 



The arterial tube where it passes under the valve D is about 

 four lines in thickness. Soon it divides into two branches of 

 smaller diameter, each of which is several yards long. One of 

 these tubes passes under the spring of the sphygmograpli, 

 which is fixed at n in such a manner that tracings may be 

 conveniently taken. Both open finally into a waste basin ; 

 but each is provided with screw clamps, by which it can be 

 compressed or constricted at any desired distance from the 

 pump. The purpose of the bifurcation is, that the observer 

 may be enabled, without interfering in any way with the con- 

 dition of the tube, of which the expansive movements are re- 

 corded sphygmographically, to vary the quantity of liquid 

 which is discharged through it per minute. To experiment 

 with the schema satisfactoril}', it is desirable to leave the 

 working of the lever to an assistant, or, still better, to arrange 

 the apparatus so that the work can be clone by an electro- 

 magnet. The observer is then at liberty to watch the effect of 

 modifications of resistance, etc., on the form of the tracings 

 while they are in progress. The most important facts to be 

 demonstrated with the aid of the schema, as above described, 

 are the following: 



1. It is shown that the artificial and the natural pulse resemble 

 each other closely, each consisting in a succession of expansive 

 and contractile movements which always occur in the same 

 order (.see Fig. 212, a). In describing these movements, it is 

 convenient to speak of the experimental tube as the artery, and 

 to assume that elevation of the lever of the sphygmograpli is 

 equivalent to expansion of the tube, and depression to contrac- 

 tion. This granted, the tracing shows that when the valve D 

 is opened, a sudden expansion of the artery takes place; that 

 so long as the heart continues to act the vessel remains full, 

 and that the cessation of the injection of liquid from behind de- 

 termines a contraction of the artery which is as rapid as the 

 previous expansion. No sooner has the artery accomplished 

 its contraction than it begins a second expansion inferior to 

 the first both in extent and rapidity ; and then finally contracts, 

 continuing to get smaller until the aortic valve again opens. 



2. It can next be shown that just as the expansion of the* 

 lever is consequent on the opening of the aortic valve, so its 

 descent is consequent (not on the closing of the valve, but) on 

 the cessation of the injection of liquid by the pump, i. e., the 

 cessation of the systolic contraction of the ventricle. To prove 

 this, I use a contrivance which will be readily understood from 



