BACTERIA IN WATER 695 



culties are enhanced when a considerable dilution of the excreta takes 

 place. Furthermore, water is by no means a favorable medium for the 

 typhoid bacillus. Russell and Fuller 1 have shown that typhoid bacilli 

 may die in water within five days, and it is unquestionable that the 

 rate of increase of these bacteria is by no means equal to that of many 

 other microorganisms for which polluted water at the temperature en- 

 countered in streams and lakes forms a much more favorable medium. 



It is thus clear that even in infected waters the number of typhoid 

 bacilli encountered can never be very great. 2 



A large number of methods for the isolation of the typhoid bacillus 

 from water have been devised. Most of the media used are identical 

 with those employed for the isolation of these bacteria from the stools. 

 These media have been discussed in the chapter dealing with the typhoid 

 bacillus. Success is rendered more likely if 10 c.c. of the water is first 

 planted into lactose-bile in fermentation tubes holding 40 c.c. After 

 48 hours at 37.5 there will be an enrichment of typhoid bacilli which 

 can be then isolated by plating in the usual manner (see p. 134 and 

 135) on Endo's medium, Conradi Drigulski or any of the other usual 

 differential media. 



A method which has proved useful in the hands of Adami and Chapin 3 

 is one which depends upon the phenomenon of agglutination. They at- 

 tempt to agglutinate the bacilli out of liter samples of water by adding 

 powerful agglutinating serum. 



Vallet and others have attempted to precipitate typhoid bacilli out 

 of water by chemical means. To two liters of water add 20 c.c. of a 7.75 

 per cent solution of sodium hyposulphite and 20 c.c. of a 10 per cent solu- 

 tion of lead nitrate. When the precipitate has settled, the clear super- 

 natant fluid is decanted and the precipitate dissolved in a saturated 

 sodium hyposulphite solution. This clear solution is then plated. Will- 

 son 4 has modified this method by adding to the water 0.5 gm. of alum 

 to each liter. The supernatant fluid is removed and the precipitate 

 plated. 



The isolation of the vibrio of cholera is less difficult than that of B. 

 typhosus, primarily because of the much greater numbers of these 

 microorganisms discharged into sewage. The number of cholera spirilla 

 in the excreta of cholera patients is enormously higher than is that of 



1 Russell and Fuller, Jour. Inf. Dis., Suppl. 2, 1908. 



2 Laws and Anderson, Rep. of Med. Officer, London County Council, 1894. 



3 Adami and Chapin, Jour. Med. Res., xl. 1904, 



4 WiUson, Jour, of Hyg., v, 1905, 



