x INTRODUCTION 



microbe which transforms the animal material supplied by 

 dead bodies and dejecta into simpler substances, nitrates, and 

 salts of ammonia, capable of assimilation by those plants which 

 supply us with food. Further, it is the microbe which renders 

 pleasant to the taste certain animal and vegetable food- 

 products, as, for example, the juice of the grape, the extract 

 of malt, cabbages, apples, and milk, transforming these 

 respectively into wine, beer, sauerkraut, cider, kephir, various 

 kinds of cheese, etc. 



Thanks to Pasteur the activity of micro-organisms was 

 established in every case of putrefaction and fermentation ; 

 and, with this fact to start from, it became more easy to tackle 

 the problem of infectious diseases. 



Putrefaction and suppuration have been recognised for cen- 

 turies as being phenomena of the same order. Decomposing 

 pus, faecal matter smelling of putrefaction, urine issuing from 

 the bladder in a state of decomposition, all indicated that an 

 illness, a state of suffering, was equivalent to an infection of the 

 body. 



Although certain microbes, such as the bacteridium of anthrax, 

 had been observed before Pasteur's great discoveries, it was only 

 as a consequence of these discoveries that the fundamental role 

 of microscopic organisms in disease was understood. The 

 labours of Lister in surgery, and of Davaine and Koch on the 

 " black blood of anthrax " first authorised the application of 

 Pasteur's doctrine to surgery and medicine. 



Pasteur himself with his pleiad of disciples was in the midst 

 of this activity, an activity which in a very few years revolu- 

 tionised medical science and endowed medicine with more 

 than one preventive vaccine such as those against anthrax and 

 rabies. 



The Pasteur school in France and the school of Koch in 

 Germany have succeeded in elucidating many medical problems 

 of the highest importance and have drawn valuable practical 

 conclusions from these. 



Thanks to all this work, work which has increased during 

 these last years in extraordinary fashion, a universe of micro- 



