THE BACTERIA OF SOIL, AIR, WATER, ETC. 1 33 



animals ; the possession of pathogenic properties creates a prob- 

 abihty in favor of their having come from some contamination 

 with animal excreta.* 



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 impaired by 

 freezing. Prudden found the bacillus of typhoid fever alive in 

 ice after more than one hundred days. However, Sedgwick 

 and Winslow have stated that when typhoid bacilli are frozen 

 in water the majority of them are destroyed.! Nevertheless, 

 it is safest to have the source from which ice is taken as care- 

 fully 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. 



Bacteria of Milk and Other Foods. J — 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 the principal food of young infants, who are highly 

 susceptible to certain bacteria, and 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; however, after milking the cow a little milk 

 generally remains in the milk-ducts and in the lower part of 

 the teat in which numerous bacteria will have developed before 



* Consult Vaughan. Journal American Medical Association. April 9, 1904. 

 For special methods of detecting the Bacillus coli communis see under this 

 bacillus, page 310. 



■f Clark. Bacterial Purification of Water by Freezing. Reports AmeTicau 

 Public Health Association. Vol. XXVII. See also Hutchings and Wheeler. 

 American Journal Medical Sciences. Vol. CXXVI., p. 680. 



J See Conn. Bacteria in Milk and its Products. 1903. Russell. Dairy 

 Bacteriology. 



