36 VACCINE AND SEEUM THERAPY 



bacteriolysins, nor are they increased by immunisation, 

 the quantity present in each leucocyte being probably 

 at all times simply sufficient for the digestion of the 

 limited number of bacteria which can be taken up by 

 the individual cell. 



Problems and Facts of Immunity in their 

 Bearing' upon the Treatment of Infectious 

 Diseases. — While dealing with the various theories 

 and facts in the previous sections, no systematic 

 attempt has been made to correlate the facts pre- 

 sented or to determine their bearing on the most vital 

 problem of all, the treatment of infectious diseases. 

 To understand this more fully, let me recall certain 

 facts, some of which are well understood — for 

 instance, the fact that certain micro-organisms, such 

 as the tetanus bacillus, secrete soluble poisons, both 

 during artificial cultivation and during their life in 

 the animal body, which poisons are highly toxic. 

 Such germs, then, once having gained a firm foot- 

 hold, and often even an insecure foothold, in the 

 animal body, are possessed of a powerful weapon of 

 offence against the sensitive physiological bases of 

 the host, and, possibly, of defence against its more 

 immediate and mobile means of combating the 

 germs themselves. 



In the case, however, of most other pathogenic 

 germs, the secretion, at least in artificial media, of 

 such highly soluble poisons has not been satisfactorily 

 demonstrated. In the case of the bacteria which 

 secrete true soluble poisons, these poisons are 



