SAOTEBIOLOGfCAL STUDY OF WATER. 591 



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 Eisner, Stoddart, or Hiss, detailed in the chapter 

 on bacillus typhosus. Personally ^ve 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 ordinary Pasteur 

 or Birkfield filter, brushing off the matters collected 

 on the filter into a sterilized vessel and examining 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. 



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- 

 course must then be had to all the differential tests 

 detailed in the chapter on that organism. 



The Quantitative Estimation of Bacteria in 



