CHAPTER XXX 



THE BACTERIA OF THE HUMAN BODY 



Introduction. The healthy human body at all -times is 

 infested or inhabited by a great variety of bacteria. In the 

 majority of cases these bacteria are harmless, although patho- 

 genic bacteria may occasionally be present. When present, 

 these pathogenic bacteria do not always necessarily enter the 

 tissues of the body and produce an infection. Bacteria are 

 present on the skin and mucous membranes and in all the cavi- 

 ties of the body which are in communication with the exterior. 

 Some species are quite constant in their presence, while others 

 are found only occasionally. It should be remembered that 

 the conditions requisite for bacterial growth are organic food, 

 a certain amount of moisture, and a temperature varying from 

 15 C. to 40 C. These conditions are all present in the 

 human body. It is possible that the non-pathogenic bacteria 

 may serve in some unknown way to protect the body against 

 invasion by the pathogenic organisms. This point has not 

 been thoroughly investigated. 



Bacteria of the Skin and Exposed Mucous Membranes. - 

 A great variety of species of bacteria and large numbers of 

 them are found on the exposed surfaces of the body. The 

 secretions of the subaceous glands of the skin and the desqua- 



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