THE CIRCULATION OF THE BLOOD. 249 



THE NERVOUS SYSTEM IN REIiATION TO THE HEART. 



The attempts to determine just why the heart beats at all, 

 and especially the share taken by the nervous system, if any 

 direct one, are beset with great difficulty ; though, as we shall 

 attempt to show later, this subject also has been cramped within 

 too narrow limits, and hence regarded in a false light. 



Till comparatively recently the frog's heart alone received 

 much attention, if we except those of certain well-known mam- 

 mals. In the heart of the frog there are ganglion-cells in vari- 

 ous parts, especially numerous in the sinus venosus (or expan- 

 sion of the great veins where they meet the auricles) ; also in the 

 auricles, more especially m the septum (ganglia of Eemak), while 

 they are absent from the greater part of the ventricle, though 

 found in the auriculo-ventricular groove (ganglia of Bidder). 



Recently it has been found that ganglion-cells occur in the 

 ventricles of warm-blooded animals. In the hearts of the dog, 

 calf, sheep, and pig, which are those lately subjected to investi- 

 gation, it is found that the nerve-cells do not occur near the 

 apex of the ventricles, but mainly in the middle and basal por- 

 tions, being most abundant in the anterior and posterior inter- 

 ventricular furrows and in the left ventricle. But there are 

 differences for each group of animals ; thus, these ganglion- 

 cells are most abundant, so far as the mammals as yet inves- 

 tigated are concerned, in the ventricles of the pig, and least so 

 in those of the dog. In the cat they are also scanty. Ganglion- 

 cells occur in the auricles, and are especially abundant near the 

 terminations of the great veins. 



It has long been known that the heart of a frog removed 

 from the body will pulsate for hours, especially if fed with 

 serum, blood, or similar fluids ; and that it may be divided in 

 almost any conceivable way, even when teased up into minute 

 particles, and still continue to beat. The apex, however, when 

 separated does not beat. Yet even this quiescent apex may be 

 set pulsating if tied upon the end of a tube, through which it 

 may be fed under pressure. 



We may here point out that the whole heart or a part of it 

 may be made to describe its action by the graphic method in 

 various ways, the principles underlying which are either that 

 the heart pulls upon a recording lever (lifts it) ; acts against the 

 fluid of a manometer ; or, inclosed in a vessel containing oil or 

 similar fluid, moves a piston in a cylinder. 



