CM. X.X. 



THE STANNIUS HEART. 



255 



the sinus, whereby the auricles and ventricle can no longer 

 continue to contract, but this suggestion must be given up if 

 the present theory as to the functions of the nerve ganglia is 

 correct. The effect of Stannius' ligature is simply an example of 

 what has been called by Gaskell blocking. The explanation of 

 this term is as follows : It appears that under normal conditions 



Fig. 252. Isolated nerve-cells from the frog's heart. I. Usual form. II. Twin cell. 

 C, capsule ; N, nucleus ; JV', nucleolus ; P, process. (From Ecker.) 



the wave of contraction in the heart starts at the sinus and 

 travels downwards over the auricles to the ventricle, the irrita- 

 bility of the muscle and the power of rhythmic contractility being 

 greatest in the sinus, less in the auricles, and still less in the 

 ventricle, whilst under ordinary conditions the apical portion of 

 the ventricle exhibits very slight irritability and still less power 

 of spontaneous contraction. Thus it may be supposed that the 



i.v.c. 



Fig. 253. Diagram of ganglia in frog's heart. R, Remak's, B, Bidder's ganglion; 

 8, sinus ; A, auricle ; V, ventricle. 



wave of contraction beginning at the sinus is more or less blocked 

 by a ring of muscle at lower irritability at its junction with the 

 auricles ; again the wave in the auricles is similarly delayed 

 in its passage over to the ventricle by a ring of lesser irritability, 

 and thus the wave of contraction starting at the sinus is broken 

 as it were both at the auricles and at the ventricle. By an 

 arrangement of ligatures, or better, of a system of clamps, one 

 part of the heart may be isolated from the other portion, and 

 the contraction when stimulated by an induction shock may be 



