106 WARFARE IN THE HUMAN BODY 



From such considerations it follows that an inquiry 

 must be made as to how the vagus acts on the heart physio- 

 logically, and what its real functions are. Such a question 

 leads to a fresh study of the heart's mechanism, and the role 

 played by the augmentor as well as the vagus. Even if 

 the notion that the vagus normally weakens the heart be 

 put aside as contradicting the whole course of evolution, 

 and if the facts can be otherwise explained when it does 

 happen to have that effect, it may, at least, be admitted 

 that it certainly slows the heart on stimulation, just as 

 the augmentor or accelerator fibres quicken it. But 

 reasonable slowness of action by no means implies weaken- 

 ing or fatigue. The heart can be slowed in many ways, 

 by the toxins of fatigue or disease, by high blood-pressure, 

 by a depletion of the higher centres owing to vaso-motor 

 action (Mackenzie) ; but if it is slowed physiologically, it 

 must be for advantageous action, and what is seen in ex- 

 periment is, at least, partially irrelevant, even if the whole 

 of the phenomena, when understood, can be linked together. 

 Following the method hitherto adopted, we may seek for 

 illustrations of slowing in something that resembles an 

 organism, and try to discover why it happens, and what it 

 effects. Let such an organism or individual be a University 

 eight. In a well-trained crew the endeavour of the trainer 

 has been to get a long, slow, " well-pulled-through " action ; 

 but when the crew become tired they are apt to accelerate 

 the stroke, and make it short and " snatchy." It is found 

 that more power is obtained by the long and slow stroke, 

 and when the coxswain or the stroke oar think it time to 

 quicken, both are well aware the reserve power of the crew 

 is being drawn upon. When the slower rate is maintained, 

 " inhibition " is the inhibition of the accelerator, not 

 inhibition of the strength of the crew. By inhibiting 



