EXAMINATION OF WATER 307 



B.proteus or ramosus), or else the B. coli would develop to an 

 extent capable of preventing the recognition of the typhoid 

 bacillus. The exception was slightly acid potato-gelatine, 

 containing 1 per cent, of iodide of potassium. The process 

 recommended is to boil potato-decoction (500 grammes to 

 1 litre of water) with 10 per cent, of gelatine. Sufficient 

 of a 2 per cent, solution of sodium hydrate is added till 

 only a faint acidity remains, litmus being used as indicator. 



Eisner found that the B. proteus and ramosus, which 

 always grow on carbolised gelatine, either never occurred 

 on this medium, or were rapidly overgrown by the colon 

 bacillus. The B. coli grew in twenty-four hours, presenting 

 the usual appearance of that organism on acid media ; the 

 B. typhosus was scarcely visible in twenty-four hours, but in 

 forty-eight hours appeared in small, shining, very finely- 

 granulated colonies like little drops of water, which con- 

 trasted strongly with the larger coarsely-granulated, 

 brownish colonies of the colon bacillus. The B. coli only 

 acquired the appearance of the typhoid colonies when a 

 great number of the organisms were present, and many, 

 therefore, grew without finding room for their proper 

 development. In plates made with weaker inoculations, it 

 is impossible to mistake one bacillus for the other. 



We have used this method with satisfactory results. 

 The colonies of the B. typhosus appear more quickly on this 

 medium than on carbol-gelatine, but otherwise this appears 

 to be the only advantage it possesses. A number of other 

 methods for the isolation of the B. typhosus and coli have 

 been proposed by different investigators. Uffelmann has 

 suggested the addition of O'l per cent, of citric acid to the 

 nutrient gelatine, to restrain the growth of the liquefying 

 organisms. Dunbar has found, however, that the amount 

 of citric acid prescribed by Uffelmann is in excess of what 

 the typhoid bacilli are capable of standing. He found that 



