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Microbes and You 



Fig. 68. Pressure-fed syringe being used to inoculate fertile eggs 

 with suspensions of living rickettsiae. {Courtesy of E. R. Squibb and 

 Sons, New York.) 



Incubation temperatures about five degrees less than that of 

 the human body (37° C.) are favorable for optimum growth of 

 rickettsiae, and this appears to bear a direct relationship to the 

 reduced metabolism of host cells at this lower temperature of 

 32° C. Raising the temperature of laboratory animals which have 



