Body Temperature Organisms. 59 



plates showed 4200 bacteria per c.c, but agar plates at 37 

 degrees were sterile. 



The body-temperature count must, of course, be made 

 upon agar plates, otherwise the procedure is the same 

 which has already been described for the routine quan- 

 titative bacteriological analysis. The period of incuba- 

 tion ordinarily adopted by the writers is twenty-four 

 hours, as little development occurs after that time. DifS- 

 culiy is sometimes caused by the spreading of colonies 

 of certain organisms over the surface of the plate in the 

 water of condensation which gathers; this may be avoided 

 by inverting the plates after the agar is once well set or 

 still better by the use of plates provided with earthenware 

 tops as suggested by Hill. The porous earthenware 

 absorbs the water which condenses on it, the surface of 

 the plate remains comparatively dry, and the percentage 

 of " spread " plates is reduced from 30 per cent to i per 

 cent (Hill, 1904). 



Additional evidence as to the character of a water 

 sample may be obtained with little extra trouble by add- 

 ing a sugar and some sterile litmus to the agar medium 

 and observing the fermenting powers of the organisms 

 present, as first suggested by Wurtz (Wurtz, 1892) for the 

 separation of B. coh from B. typhi. It happens that the 

 most abundant intestinal organisms, belonging to the 

 groups of the colon baciUi and the streptococci, decom- 

 pose dextrose and lactose with the- formation of a large 

 excess of acid. The decomposition of the latter sugar 



