304 APPLIED BACTERIOLOGY 



volume of the water to examination. This object is attained 

 by concentrating the bacterial contents of the water by 

 passing 1,000 to 3,000 c.c. or more of the sample through a 

 small sterile Pasteur-Chamberland filter. By this treat- 

 ment all the bacteria in the water are retained on the outer 

 surface of the filter. The particulate matter thus retained 

 is then brushed off the outer coating of the filter with a 

 sterile brush or sponge into about 20 c.c. of sterile distilled 

 water. One c.c. of this concentration, which contains the 

 particulate matter representing from 50 to 150 c.c. of the 

 original water, is then immediately submitted to plate 

 culture by one of the undermentioned methods, to isolate 

 the colon bacillus and also the B. typhosus, if present. 



1. Inhibition by Means of Phenol. — The B. typhosus and 

 the B. coli communis are among the limited number of 

 micro-organisms which will grow in the presence of small 

 quantities of phenol, which addition retards or inhibits the 

 common water bacteria, such as the B. fluorescens lique- 

 faciens, Proteus vulgaris, B. mesentericus, etc., the presence 

 of which would liquefy the gelatine, and by their rapid 

 growth would annihilate the B. typhosus, if present. The 

 presence of a small quantity of phenol does not in any way 

 interfere with the growth of the B. typhosus or the B. coli 

 communis, but exhibits a marked inhibitory effect upon the 

 common water bacteria, and, by the retardation and sup- 

 pression of these, the colonies of the B. typhosus and the 

 B. coli communis have a chance and leisure to appear. 



The use of phenol for this purpose appears to be due, 

 in the first instance, to Chantemesse and Widal,* who used 

 nutrient gelatme containing 0-25 per cent, of phenol. 

 Thoinot,t a little later, inhibited the growth of organisms 

 other than the typhoid and colon bacilli, by adding 0*25 

 per cent, of phenol to the water under examination, which 



* Gazette des Eopitaux, 1887, p. 202. f Ibid., p. 384. 



