BACTERIOLOGICAL STUDY OF WATER. 597 



made. To each are then added from 1 to 3 c.c. of the 

 water, and they are placed in the incubator at body-tem- 

 perature. It is said that whatever development occurs 

 consists only of the typhoid or colon bacillus, or both, if 

 they were present in the original sample. They may 

 then be isolated and separated by the usual plate method, 

 or, better still, through the application of the methods 

 of v. Drigalski and Conradi, of Ficker, or of Hoffmann 

 and Ficker, or several of these methods in conjunction, 

 detailed in the chapter on bacillus typhosus. Personally 

 we have not had much success with the Parietti method. 

 The typhoid bacillus has been isolated from water by 

 passing very large quantities of water through an ordi- 

 nary Pasteur or Berkefeld filter, brushing off the matters 

 collected on the filter into a sterilized vessel and examin- 

 ing this by plate methods. 



It has occurred to us that possibly the employment 

 of chemical coagulants, such as alum and iron, might 

 prove serviceable for this purpose. Their action would 

 be to mechanically drag down, in precipitating as hy- 

 droxides, the suspended bacteria contained in the fluid. 

 This precipitate could then be examined bacteriologi- 

 cally, instead of the water, and the recent experiments 

 of Ficker (loc. cit.) appear to demonstrate the value of 

 such a procedure. 



The difficulties in this field of work are obviously 

 due to the suspension of a very small number of the 

 disease-producing organisms sought for in large volumes 

 of fluid, and the association with them of large numbers 

 of other species that offer a very great obstacle to the 

 successful search for the pathogenic varieties. 



If by either of the above procedures bacilli that bear 

 any resemblance to bacillus typhosus be isolated, re- 



