VACCINATION. 37! 



attacks of micro-organisms on the body is entirely due to the 

 action of the amoeboid cells of the body, that these cells are 

 living pieces of protoplasm, that they are constantly taking 

 into their own substance all foreign particles which find their 

 way into the body, that wherever there is an extra demand on 

 their energies, a large number are attracted to the point at 

 which the work is to be done, and that these cells acting on 

 the micro-organisms just as they do on foreign bodies, take 

 them up into their substance, digest and convert them 

 partly to their own uses, and gradually throw into the circu- 

 lating fluids of the body small quantities of effete substances 

 which are removed by the ordinary physiological channels. 

 Some observers, however, hold that the process is not so 

 simple as it would appear ; certain bacteria secrete substances 

 which appear to exert a paralysing effect on the cells, and 

 may so alter them that they are unable to perform their 

 proper functions ; whilst, on the other hand, the cells secrete 

 in the performance of their work a material which has an 

 unfavourable influence on the activity of the bacteria. This 

 at first sight is an extremely feasible explanation, but when 

 we come to consider more carefully the conditions under 

 which immunity against diseases is conferred, we find that, 

 although in certain cases an attack of one disease protects 

 against an attack of a more serious and deadly malady, this 

 occurs only within certain definite and well-defined groups 

 of diseases ; there appears, therefore, to be something more 

 than a mere general protective influence generated within 

 the body. We must have specific powers of resistance 

 developed in or by the cells in order that they may be able 

 to resist specific bacterial activities, and the effects of specific 

 bacterial poisonous products. I have in previous chapters 

 spoken of the effects of the bacteria and of their products in 

 protecting against the various diseases to which they them- 

 selves give rise ; it may now be well to give a concrete 

 example of the theories that have been advanced as to the 

 nature of this protective inoculation ; let us take the develop- 

 ment of the methods that have been devised for protecting 

 animals against anthrax. 



It was found that on devitalizing the anthrax organism 

 by one of several methods it might be introduced into the 

 subcutaneous tissue of a sheep without giving rise to any 

 very serious symptoms. The first note that the virulence 



