130 THE CIRCULATION. 



described in the chapter on the NERVOUS SYSTEM ; and 

 it will appear probable that the chief peculiarity of the 

 heart, in this respect, is due to the number of its ganglia, 

 and the apparently equal power which they all exercise ; 

 so that there is no one part of the heart whose action, more 

 than another's, determines the actions of the rest. Thus, 

 if the heart of a reptile be bisected, the rhythmic, suc- 

 cessive actions of auricle and ventricle will go on in both 

 halves: we therefore cannot say that the action of the 

 right side determines or regulates that of the left, or vice 

 versa ; and we must suppose that when they act together 

 in the perfect heart, it is because they are both, as it were, 

 set to the same time. Neither can we say that the auricles 

 determine the action of the ventricles ; for, if they are 

 separated, they will both contract and dilate in regular, 

 though not necessarily similar, succession. A fact pointed 

 out by Mr. Maiden shows how the several portions of each 

 cavity are similarly adjusted to act alike, yet independently 

 of each other. If a point of the surface of the ventricle 

 of a turtle's or frog's heart be irritated, it will immediately 

 contract, and very quickly afterwards all the rest of the 

 ventricle will contract ; but, at the close of this general 

 contraction, the part that was irritated and contracted first, 

 is slightly distended or pouched out, showing that it was 

 adjusted to contract in, and for only, a certain time, and 

 that therefore as it began to contract first, so it began to 

 dilate first. 



The best interpretation, perhaps, yet given of it, and 

 of rhythmic processes in general, is that by Mr. Paget, 

 who regards them as dependent on rhythmic nutrition, i.e., 

 on a method of nutrition in which the acting parts are 

 gradually raised, with time-regulated progress, to a certain 

 state of instability of composition, which then issues in tlie 

 discharge of their functions, e.g., of nerve-force in the case 

 of the cardiac ganglia, by which force the muscular walls 

 are excited to contraction. According to this view, there is 



