174 STUDIES IN ADVANCED PHYSIOLOGY. 



There is, of course, considerable difficulty in making ex- 

 tended observations on the heart of mammals, but it is quite 

 easy to make such observations on cold-blooded forms, 

 especially on the frog and terrapin. If, now, a frog's heart 

 be carefully examined for nerves, two clumps of ganglia 

 may be found, one clump lying near the opening of the 

 large veins, in the so-called sinus. These ganglia are 

 called after their discoverer, the ganglia of Remak. The 

 second clump of ganglia lies in the septum of the auricles 

 close to the auriculo- ventricular valves. These ganglia are 

 called the ganglia of Bidders. The apex of the ventricle is 

 entirely free from nerve cells. As has been stated, such a 

 heart properly treated will continue beating for days with 

 its regular rhythm. If, now, the portion containing the 

 ganglia of Remak be cut away from the rest of the heart, 

 the heart stops beating at once, while the sinus which still 

 contains the ganglia of Remak continues its beat without 

 interruption. This observation was first made by Stannius, 

 and is still spoken of as the experiment of Stannius. 



It would seem that the only way to explain this would 

 be to assume that the ganglia of Remak are automatic 

 ganglia which produce the beating, and that the other 

 ganglia are stimulated reflexly by these. For if a heart so 

 severed from the ganglia of Remak be stimulated in some 

 mechanical way it will beat for a while more or less irregu- 

 larly, but soon comes again to a standstill. This experi- 

 ment then would seem to be a clear assurance that the beat 

 of the heart is inaugurated by the ganglia of Remak, and 

 is therefore of a purely nervous origin. The function of 

 the ganglia of Bidders could be explained by supposing that 

 they were stimulated by the ganglia of Remak, and so the 

 contraction carried into the ventricles. But there are many 

 facts which will not admit of such a simple solution to the 

 problem. If, for instance, the apex of the heart, which of 

 course contains no nerve cells, be cut off from the rest of 

 the heart it may be made to beat regularly. Here, of course, 

 is a clear case that the beat is not due to nervous influence. 



