144 MANUAL OF BACTERIOLOGY. 



Detection of Bacillus coli communis in Water. To each of a number 

 of fermentation-tubes containing i per cent, dextrose-bouillon add some 

 of the suspected water (.1 to I c.c.). Place in the incubator. Each day 

 mark the amount of gas that has formed in the closed arm. In three 

 days B. coli communis should render the bouillon strongly acid and 

 produce 50 per cent, of gas (or about that amount). From tubes show- 

 ing these characters, plates may be made and the usual tests for the 

 colon bacillus applied. 1 (See Part IV.) 



Ice. The bacteriological examination of ice differs in 

 no respect from that of water. Although development may 

 be arrested, the vitality of bacteria is not necessarily im- 

 paired by freezing. Prudden found the bacillus of typhoid 

 fever alive in ice after more than one hundred days. How- 

 ever, Sedgwick and Winslow have stated that when typhoid 

 bacilli are frozen in water the majority of them are de- 

 stroyed. Nevertheless, it is safest to have the source from 

 which ice is taken as carefully scrutinized as that of the 

 water-supply, especially in view of the universal habit of 

 cooling water in the summer time by adding ice directly to 

 the water. It is better to cool water and articles of food by 

 surrounding the vessels containing them with ice. 2 



Bacteria of Milk and Other Foods." Of the different 

 food substances, milk is probably the most important from 

 a bacteriological point of view. In the first place, most 

 other foods are cooked before eating. Furthermore, cow's 

 milk constitutes a large part of the food of many young 

 infants who are highly susceptible to certain bacteria, or to 

 substances in the milk itself, after it has undergone certain 

 alterations due to bacteria. The milk of the healthy cow 

 as it- is secreted in the mammary gland is sterile; how- 

 ever, after milking the cow a little milk generally remains 



1 T. Smith, American Journal Medical Sciences, Vol. no, 1895. 



3 Clark, " Bacterial Purification of Water by Freezing," Reports Amer- 

 ican Public Health Association, Vol. XXVII. , 1901. 



3 See Conn, " Bacteria in Milk and its Products," 1903. Russell, 

 " Dairy Bacteriology." 



