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A TEXTBOOK OF PHYSIOLOGY 



twenty-eight hours after death, the heart of a cat after freezing and 

 thawing. Nervous tissue dies quickly. 



7. Certain molluscs, arthropods, and tunicates, have automatic 

 hearts containing no ganglion cells. 



For muscular conduction of the excitatory wave there is also a 

 considerable array of evidence : 



1. With the discovery of the A.-V. bundle there is now no histo- 

 logical reason against it; in fact, experiments upon this bundle show 

 that its destruction by cutting, ligaturing, or clamping, produce 

 allorhythmia a different rhythm in auricles and ventricles, the 



FIG. 46. FIGURE SHOWING T 2 , THE POINT OF PRIMARY NEGATIVITY, AS STUDIED 

 BY THE STRING GALVANOMETER, TO VARIOUS LEADS FROM OTHER PARTS OF THE 

 HEART. THE EXCITATORY. WAVE THEREFORE STARTS FROM T 2 . T ARE LEADS 



FROM T^INIA, S FROM SlNUS, A FROM AURICLE. (T. Lewis.) 



auricles beating considerably quicker than the ventricles (Fig. 44). 

 By gradual compression of the bundle, varying degrees of arhythmia 

 can be produced before this allorhythmia is brought about. Recent 

 work with the string galvanometer has shown that the excitatory 

 wave follows the course of the A.-V. bundle. The impulse reaches 

 the inside of the ventricular wall where the A.-V. bundle arborizes 

 before it reaches the outer surface. It also reaches the outer surface 

 in the neighbourhood of the moderator band before it reaches parts 

 of the ventricular wall nearer the A.-V. groove (Fig. 45). 



Clinically, disease of the A.-V. bundle leads to an allorhythmia 

 Stokes-Adams' disease or heartblock (Fig. 42). Whether allo- 

 rhythmia induced by absolute destruction of the A.-V. bundle ever 



