Quantitative Bacteriological Examination. 41 



cordance with the directions of the Standard Methods 

 Committee. 



Even the standard procedure fails to ensure uniformity 

 in one important respect. The meat infusion Vwhich it 

 calls for is in itself a highly variable quantity. Gage and 

 Adams (1904), in the examination of fifteen lots of beef 

 infusion, found variations of nearly one per cent in organic 

 solids (calculated on the weight of the whole infusion), 

 after the final filtration. The organic constituents of the 

 meat infusion varied, therefore, among themselves by 

 nearly the total amount of peptone added. It is to be 

 hoped that the standard methods may soon be so revised 

 as to eliminate this necessarily uncertain constituent of 

 nutrient media. Criticisms of detail must, however, give 

 way to the importance of securing fairly comparable 

 results; and the confusion which would follow the use by 

 individual bacteriologists of media made without meat 

 would outbalance the errors inherent in the standard 

 procedure. 



Incubation. — Incubation should take place in a dark, 

 well-ventilated chamber where the temperature is kept 

 substantially constant at 20 degrees and where the atmos- 

 phere is practically saturated with moisture. It has been 

 shown by Whipple (Whipple, 1899) and others that the 

 number of bacteria developing in plate cultures is to an 

 appreciable extent dependent upon the presence of abun- 

 dant oxygen and moisture. Thus, reckoning the number 

 of bacteria developing in a moist chamber at 100, the 



