X MICRO-ORGANISMS IN WATER 



enunciated by Liebig was completely broken down by 

 the classical researches of Pasteur, by whom it was 

 shown that the processes of fermentation and putre- 

 faction were due, not to decomposing organic matter, 

 but to living organisms, and that living organisms were 

 also certainly the cause of some, and probably of all, 

 zymotic diseases. The presence of organic matter in 

 water was thus deprived of much of its direct import, 

 the chief interest still attaching to it being that it might 

 serve as an indication of the possible presence of living 

 organisms endowed with virulent properties, whilst the 

 interest attaching to the presence of micro-organisms 

 in water was further greatly enhanced by the proof 

 which was furnished by medical men that some zymotic 

 diseases are undoubtedly communicated by drinking 

 water. In the case of two diseases, at any rate, the 

 evidence may be regarded as conclusive on the main 

 point, and the communicability of Asiatic cholera and 

 typhoid fever by water forms one of the cardinal 

 principles of modern sanitary science, which year by 

 year is becoming more widely recognised and more 

 generally accepted. The germ theory of zymotic 

 disease, which has gained with each successive decade 

 of the past half-century a firmer hold on enlightened 

 public opinion, was naturally soon impressed into the 

 service of those who sought to explain the empirical 

 fact that these particular diseases are frequently com- 

 municated by water. 



Having thus become so early interwoven with the 

 consideration of potable waters, it is easy to under- 

 stand how the acceptance of this germ theory of disease 



