EXAMINATION OF ■WATER 399 



by the addition of phenol, leaving 5,000 to be dealt with 

 by plating out. There would obviously be no advantage 

 in concentrating such a water, since it is impossible to deal 

 satisfactorily with a plate of ordinary size containing 1,000 

 colonies. It would then be necessary to subculture every 

 one of these colonies, for the naked-eye appearances are not 

 to be relied upon. 



In practice, however, we prefer to use simple carbol- 

 gelatine containing 0'05 per cent, of phenol. This quantity 

 is quite sufficient to restrain the growth of liquefying 

 organisms, and, moreover, with this quantity there is less 

 danger of losing the typhoid bacillus if it is present. 



2. Eisner's Method. — Dr. Eisner, of Berlin, has recently 

 published* the results of an investigation made to ascertain 

 the possibility of an early recognition of enteric 'fever by 

 the bacteriological examination of the stools. He has been 

 able to recognise the Eberth-Gaffky bacillus in some cases 

 in as short a time as forty-eight hours. Dr. Eisner went 

 over the existing methods for the separation of the B. 

 typhosus and coli, with no better results than have previ- 

 ously been obtained. In all cases but one he found that 

 either persistent organisms other than those sought to be 

 isolated would grow to a sufficient extent to spoil the plate, 

 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 

 * Zeitschr. /. Hyg., xxi. 1. 



