THE BACTERIOLOGIC EXAMINATION OP MILK 



421 



These colonies can be rapidly counted and the number of bacteria 

 per cubic centimeter calculated." 



The author has designed a special water-bath, a nivellating 

 apparatus, and an incubating cabinet for executing his method 

 (Figs. 186-188). 



Fig. 186. — ^Warm box of water-bath, kept at 45° C, used to keep the 

 little plates warm while the agar is being spread. (Frost, in Jour. Amer. 

 Med. Assoc, vol. 66, 1916.) 



Since quick results are under some conditions desirable, at- 

 tention has recently been given to bacterial enumeration by direct 

 microscopic examination. This is really a revival of the first 





Fig. 187. — Incubating cabinet. Little plates are kept moist during 

 incubation. Cabinet is put in incubator. (Frost, in Jour. Amer. Med. 

 Assoc, vol. 66, 1916.) 



attempts made to count bacteria. Before the plate method was 

 evolved numbers were estimated by direct observation. A micro- 

 scopic method for enumerating bacteria in sewage was devised 

 by Winslow in 1905, while Slack was the first to apply the method 



