172 The Story of the Bacteria 



fostered as plants and animals slowly rose to 

 higher types. 



But beyond this we have found out that we 

 can secure an artificial cell adaptation by 

 proxy in the horse, and through his cells, 

 educated for the occasion, secure the precious 

 juices which not only can confer immunity 

 upon the well, but can save those already 

 stricken. In these and many other ways 

 which we have but glanced at in passing, 

 we can reinforce to-day the subtle safeguards 

 of the body against the minute incitors of 

 infection. 



If we compare our knowledge of infectious 

 diseases to-day with that which was current 

 twenty-five years ago, it is evident that an 

 advance has taken place which is fairly 

 revolutionary. Then we did not even know 

 what caused most of the infections. The 

 efforts to cure them were uncertain and in- 

 effective, and preventive measures were largely 

 futile. To-day we know what the causes of 

 most of these diseases are, how the recupera- 

 tive forces of the body meet them, in many 

 instances what we can do to help these forces, 



