258 COMPARATIVE PHYSIOLOGY. 



the heart's rhythm has become very slow, also point to influ- 

 ences of a central origin as greatly affecting the life-processes 

 of this organ. 



It has been shown that the vagus nerve in some cold-blooded 

 animals, as is probable also in the higher vertebrates, consists 

 of two sets of fibers— those which are inhibitory proper and 

 those which are not, but belong to the sympathetic system. 



Separate stimulation of the former favors nutritive processes, 

 is preservative ; of the latter, destructive. This has been ex- 

 pressed by saying that the former favors constructive (anabolic) 

 metabolism ; the latter destructive (katabolic) mietabolism. It 

 is assumed that all the metabolism of the body may be repre- 

 sented as made up of katabolic following anabolic processes. 



Whether such a view of metabolism expresses any more 

 than a sort of general tendency of the chemistry of the body 

 is doubtful. It is a very simple representation of what in all 

 probability is extremely complex ; and if it be implied that 

 throughout the body certain steps are always taken upward in 

 construction to be always afterward followed by certain down- 

 ward destructive changes, we must reject it as too rigid and 

 artificial a representation of natural processes. 



We think, however, that, upon all the evidence, pathological 

 and clinical as well as physiological, the student may believe 

 that the vagus nerve, like the other nerves of the hody, accord- 

 ing to our own theory, exercises a constant beneficial, guiding 

 — let us say determining — influence over the metabolism of the 

 organ it supplies ; and we here suggest that, if this view were 

 applied to the origin and course of cardiac disease, it would 

 result in a gain to the science and art of medicine. 



THE ACCELERATOR (AUGMENTOR) NERVES OF THE 



HEART. 



It has been known for many years that in the dog, cat, 

 rabbit, and some other mammals, there are nerves proceeding 

 from certain of the ganglia of the sympathetic chain high up, 

 stimulation of which lead to an acceleration of the heart-beat. 

 Very recently these nerves have been traced in a number of 

 cold-blooded animals, and the whole subject placed on a broader 

 and sounder basis. 



There are variations in the distribution of these nerves for 

 different groups of animals, but it will suffice if we indicate 



