312 



THE NERVOUS REGULATION OF THE HEART 



a spinal cardio-accelerator center. It may be surmised that this spinal 

 center is controlled in turn by a higher center located in the medulla 

 oblongata near the cardio-inhibitor center. These spinal accelerator 

 fibers finally reach the ganghon stellatum by way of the white rami 

 communicantes (dog) and pass by way of the annulus of Vieussens to 

 the inferior cervical ganghon. Their terminals are to be found in these 

 ganglia, where they form synapses with other cells. Fresh relays of 

 non-meduUated fibers continue onward through the cardiac plexus to 

 the musculature of the heart. The latter connection seems to be 

 effected without the intervention of intracardiac nerve cells, while the 



inhibitor fibers, as has been mentioned 

 above, are intimately associated with 

 Remak's as well as with other intrinsic 

 ganglia of the heart. The accelerator 

 fibers may be stimulated at almost any 

 point of their course. Very favorable 

 conditions prevail in the cat in which 

 animal a distinct nervus accelerans ex- 

 tends between the stellate ganglion and 

 the cardiac plexus. 



The Character of the Inhibition. — 

 If a moderate mechanical, chemical, or 

 electrical stimulus is applied to the in- 

 tact vagus, the normal rhythm of the 

 heart soon gives way to a much slower 

 one. The strength of the stimulus 

 may then be increased until this organ 

 becomes more and more diastolic and 

 Fig. 163.— Sketch TO Show THE finally ceases its activity altogether. 

 Accelerator (and Augmentor) A functional diminution of this kind, 



Branches FROM THE Stellate Gang- ^j. inhibition, as it Is COmmonly called, 

 LION (in the Cat, Left Side). , , , • i , -, - ,, • 



1. the ventral branch of theannu- ^^^ ^^ obtamed by applymg the Stimu- 



lus (ansa subclavia) ; 2, small branch lus tO any pomt of this nerve, in fact, 



not constantly present; 3, Boehm's even to its nucleus in the meduUa. 



accelerator nerve (N. cardiacus and tt j j- j-x- u 



ganglion stellatum). {HowelL) Under Ordinary conditions, however, 



its cervical portion is selected for the 

 excitation, because it is more accessible than its cranial or thoracic 

 portions. It should also be remembered that the inhibitor mechan- 

 ism is not equally receptive or sensitive in all animals, and secondly, 

 that the inhibitor power of the right and left vagi differs some- 

 what even in the same animal. Thus, it is rather diflftcult to cause 

 a complete arrest of the heart of the cat, while it is comparatively 

 simple to attain this result in the dog. Quite similarly, it is often 

 impossible to cause an inhibition with the aid of one vagus, while the 

 stimulation of the opposite nerve gives an almost immediate maximal 

 effect. In frogs, turtles, and snakes, the right nerve is generally 

 the stronger, while in those mammals which are usually used for 



