396 APPLIED BACTERIOLOGY 



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 jB. 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. fiuorescens 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 

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

 the B. coli com,m,unis 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 gelatine containing 0*25 per cent, of phenol. 

 Thoinot,-f- 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 

 was then incubated at blood-heat and the water afterwards 

 plate-cultured. 



As pointed out by Holz, and confirmed by Dunbar, the 

 above authors use a percentage of phenol which altogether 

 prevents the growth of the B. typhosus. Dunbar states 

 that 0"12 per cent, of phenol greatly interferes with the 



* Gazette des Hdpitaux, 1887, p. 202. t Ibid., p. 384. 



