PREFACE ix 



part the regular and steady control which they pre- 

 viously exercised on the metabolism of the tissues, 

 including the excretory processes, and thus the 

 general vitality is diminished. But if after the first 

 period of excitement the nerve-centres regain little by 

 little their normal mode of functioning in the very 

 presence of the bacteria, or if they have done so 

 before in the presence of an allied but less virulent 

 genus, a second attack is not likely to lead to the same 

 degree of commotion and relaxation in the nerve- 

 cells, or, in - other words, to the same amount of 

 disturbance in the nervous metabolic rhythm. When 

 in vaccination the lymph is introduced into the arm, 

 a local disturbance of the metabolic processes takes 

 place. In ^a few days' time there may be swelling of 

 the part and other signs of inflammation. As matters 

 develop, especially if the case be severe, the effect 

 becomes more general, and slightly feverish symptoms 

 may be noticed. Thus both locally and as a whole 

 the nervous system comes under this new influence. 

 Its' environment is modified, but in spite of the 

 baneful character of this modification it continues to 

 function. Within three or four weeks from the date 

 of vaccination all the bacteria have been worsted in 

 their attack upon the system. They have disappeared, 

 being either absorbed by leucocytes or excreted by the 

 usual channels. As an active force in the body they 

 have ceased to exist. That anything of a tangible 

 nature beyond the scar remains after the fourth week 

 is indeed highly improbable, and as time goes on the 



