CHAPTER IV. 



DETERMINATION OF THE NUMBER OF ORGANISMS 

 DEVELOPING AT THE BODY TEMPERATURE. 



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 containing much decaying vege- 

 table matter they occur in abundance. Other meta- 

 trophic 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 developing most actively 

 at the temperature of the human organism, 37° C, which 

 altogether checks the growth of the majority of normal 

 earth and water forms. The determination of the num- 

 ber of organisms growing at the body temperature may 

 throw light, then, on the presence of direct sewage pollu- 

 tion, since the bacteria from the alimentary canal flourish 



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