MOISTURE 51 



This applies to the morphological features described in 

 Chapters II to IV and to all the physiological activities 

 discussed in Chapters IX to XII. It is also fundamental 

 in the discussion of disinfection and sterilization in Chapters 

 XIII to XV, to the study of bacteria as treated in Part III 

 and is no less applicable to Pathogenic Bacteriology to 

 which Part IV forms an introduction. 



Numerous articles appear even yet in bacteriological 

 literature in which the sole conclusion is that the organism 

 studied showed variations from the assumed normal under 

 a given set of conditions. 



The fact of variation with changes in environmental 

 conditions should be axiomatic with the bacteriologist and 

 no more work needs to be done to establish it. 



On the other hand far too little has been done on a quan- 

 titative determination of the limits of any one of these condi- 

 tions and on the range throughout which little variation is 

 detectable. Many of these determinations for particular 

 organisms have a most valuable practical as well as scientific 

 application. This field is reserved for special bacteriology 

 and does not come within the limits of this text-book which 

 is concerned with having the student well grounded in 

 fundamentals. 



MOISTURE. 



The maximmn moisture is absolutely pure water, and no 

 organism can thrive in this alone owing to the factor of too 

 low osmotic pressure and to the further factor of absence of 

 food material. There are many bacteria, which thrive in 

 water containing only traces of mineral salts and a large 

 class whose natural habitat is surface water. These "water 

 bacteria" are of great benefit in the purification of streams. 

 They are as a class harmless to men and animals. Some 

 of the disease-producing bacteria, like Eberthella typhi 

 (of typhoid fever) and Vibrio comma (of Asiatic cholera), 

 were undoubtedly originally water bacteria, and it is rather 

 striking that in these diseases conditions are induced in 

 the intestine (diarrheas) which simulate the original watery 

 environment. The miiiimum moisture condition is abso- 



