696 BACTERIA IN AIR, SOIL, WATER, AND MILK 



coli, however, withstands these reagents as well as B. typhosus, or even 

 better, these methods have not met with great success. 



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

 is one which depends upon the phenomenon of agglutination. These 

 authors collect water in two-iiter specimens and to each two liters add 

 20 c.c. of one per cent glucose broth. These samples are incubated at 

 37.5° C. for twenty-four hours, and at the end of this time quantities 

 of 10 c.c. are withdrawn and placed in test tubes. To each of these 

 tubes potent typhoid serum, preferably diluted 1 : 60, is added, and 

 whenever agglutination occ\u-s the flocculi are washed and plated on 

 various media for identification. 



Vallet and others have attempted to precipitate typhoid bacilli out 

 of water by chemical means. The pm-pose of these methods has been 

 to entangle the bacteria in an inert precipitate, and thus concentrate the 

 bacteria in water for purposes of cultivation. Vallet's method is as 

 follows: 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 solution of lead 

 nitrate. When the precipitate has settled, the clear supernatant fluid 

 is decanted and the precipitate dissolved in a saturated sodium hypo- 

 sulphite solution. This clear solution is then plated. Willson ^ has 

 modified this method by adding to the water 0.5 gm. of alum to each 

 liter. A precipitate is formed which may either be allowed to settle or 

 may be brought down by centrifugalization. The supernatant fluid is 

 removed and the precipitate plated. 



In actual work many of the methods which are aimed purely at B. 

 coli may lead to success in the isolation of B. typhosus, because of 

 the similarity of the two organisms in their reaction to definite media. 

 Thus, the method of Jackson,^ who employs one per cent of lactose in 

 pure ox-bile for the isolation of B. coli, has occasionally led to the simul- 

 taneous isolation of B. typhosus. 



The isolation of the vibrio of cholera is less difl&cult 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 

 B. typhosus in the stools of typhoid-fever patients. It is not infre- 

 quent, therefore, that the source of a cholera infection may be directly 

 traced to the water supply. Koch,^ the discoverer of the cholera vibrio, 



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



2 Willson, Jour, of Hyg., v, 1905. 



5 Jacksm Joum. of Inf. Dis., Suppl. 2, 1907. ' Koch, Zeit. f . Hyg., xiv, 1893. 



