CHAPTER IV 



DETERMINATION OF THE NUMBER OF ORGANISMS 

 DEVELOPING AT THE BODY TEMPERATURE 



Relation between Counts Made at 20 and 37. The 



count of colonies upon the gelatin plate measures, 

 as we have pointed out, the number of the metatrophic 

 bacteria in general; and the distribution of these forms 

 corresponds with the decomposition of organic matter 

 wherever it may occur. In this great class, there are 

 some species which will grow under a wide variety of 

 conditions. These are present in most waters in small 

 numbers, and in sources contaminated with wash from 

 decaying vegetable matter they occur in abundance. 

 Other metatrophic forms, however, through a semi- 

 parasitic mode of life, have become specially adapted 

 to the peculiar conditions characteristic of the animal 

 body; and these bacteria possess the property of develop- 

 ing most actively at the temperature of the human 

 body, 37 C., which altogether checks the growth of 

 the majority of normal earth and water forms. The 

 determination of the number of organisms growing 

 at the body temperature may throw light, then, on the 

 presence of direct sewage pollution, since the bacteria 

 from the alimentary canal flourish under such con- 

 ditions, while most of those derived from other sources 

 do not. Savage classifies the bacteria which may 



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