104 WARFARE IN THE HUMAN BODY 



atque rotundus, it is a function of the two variables — stimulus, 

 and the condition of the stimulated organism. It may be 

 little or more and more. The further it is considered the 

 more justifiable it appears to regard it as a stimulus pro- 

 ducing pathological effects, and such views are in keeping 

 with the notion that the vagus normally is not " depressor," 

 but, being a most delicate adjustment agent, can easily 

 become such. We can certainly imagine that its action is 

 depressing if all the vagus fibres are excited at once, which 

 probably never happens in physiological conditions. So 

 very rarely can all the fibres of the biceps be excited 

 together. There are nearly a thousand fibres in its trunk. 

 If the violent tonic spasm, produced by strong electric 

 stimulation, excites them all together the phenomenon is 

 explicable. Otherwise we must assume, as said above, 

 what no physiologist seems to believe, that energy does 

 really pass over from the end-plate into the muscle itself. 



If then shock be a complex of such phenomena, and 

 if it is hard to conceive that evolution has made physio- 

 logical stimulation of the vagus a means of destruction, 

 it necessarily follows that its experimental stimulation, 

 leading to weakening and failure of the heart, is essentially 

 pathological, and that from what occurs no legitimate 

 physiological deductions can be drawn. The Webers 

 discovered an interesting fact ; but all they noted 

 must be classed as pathological or traumatic. Doubt is 

 thus thrown upon the view that the vagus can weaken a 

 muscle in one place and stimulate it in another. Nothing 

 will co-ordinate the facts but some proof, or suggestion 

 of proof, that the vagus exerts both on heart muscle and 

 smooth muscle an " influence " which helps both to 

 function better. 



What then is the real function of the cardiac vagus ? 



