OF VITAL MOTION. 119 



vessels if these cavities were fully dilated. In ple- 

 thora, on the contrary, the pulse is generally full and 

 slow ; and hence we should argue, in the first place, 

 that the diastole is perfect, and a large quantity of 

 blood taken into the heart at this time ; and secondly, 

 that the presence of the blood does not immediately 

 and of necessity give rise to a systole. Comparing, 

 indeed, the state of plethora with that of anaemia, the 

 contrary would seem to be the fact, and the rapid 

 systole in the one case would seem to be ascribable to 

 the small quantity of blood which is taken into the 

 heart, together with its impoverished and watery 

 quality ; and the deferred systole, in the other case, to 

 the presence of a larger quantity of richer and more 

 genial blood. The effects, indeed, are analogous to those 

 witnessed in the vessels under similar circumstances, 

 and it must be admitted that the heart has a greater 

 capacity of dilatation in plethora than in anaemia. 

 And so clear in other respects is the significance of the 

 same facts, that it seems as reasonable to suppose that 

 the blood excites the vessels of erectile tissue to contrac- 

 tion, as that it has this influence upon the heart, which 

 after all, is but one of many forms of bloodvessel. 



It would appear, also, on further examination that 

 the influence of the blood is an agent of extreme 

 importance in determining the rhythmical action of 

 the heart. At the ventricular systole the blood is 

 distributed to the vessels, and among the rest to the 



