246 MILK HYGIENE 



for proper development, 10 c.c. of agar shall be used 

 for each plate. In plating a large number of samples 

 at one time the dilution and transfer of diluted milk to 

 the plates may be done for four or eight samples, then 

 the agar poured, one tube to each plate, then another 

 eight samples diluted, etc. 



Incubation. Concerning incubation two methods are 

 at present in use. Three-fifths of the laboratory work- 

 ers consulted recommended incubation at 37 C. for 

 twenty- four hours with saturated atmosphere, the re- 

 maining two-fifths allowed varying lengths of time at 

 different degrees of room temperature and at whatever 

 degree of humidity happened to obtain. 



When considering these two methods many advan- 

 tages of the method of incubation at 37 C. are evident, 

 including the ease of maintaining this temperature in 

 any laboratory, the evident uniformity of counts so ob- 

 tained in different places as compared with those 

 obtained by the varying methods of technique, as to 

 temperature and incubation period, where room tem- 

 perature is employed, and the quickness with which 

 results are obtained, doing away with large accumula- 

 tions of uncounted plates. 



Forty-eight hour plates grown at 37 C. give a 

 slightly higher count, not enough higher to materially 

 change the report, while the loss by " spreaders " is 

 increased and the count delayed. 



To secure saturation of the atmosphere the incubator 

 should be made with a shallow depression over the whole 

 bottom surface, which may be kept filled with water, or 

 in default of this a large shallow pan of water may be 

 kept on one of the lower shelves. 



Much work will be done on comparison of 37 C. and 

 "room temperature " during the coming year. 



Counting: Expression of results. Since minor dif- 

 ferences in milk counts are within the working error of 

 the methods and are of no significance in practice, the 

 following scale has been adopted for recording results 

 of market milk examinations : 



Counts below 100,000 are distinguished by ten 

 thousands. 



