Report on the Bacteriology of Water. 451 



water bacteria, and as to the more rapid disappearance of the typhoid 

 bacilli. The directly prejudicial action of the salt on the typhoid 

 bacillus was farther demonstrated by the addition of salt to steam- 

 sterilised Thames water containing typhoid bacilli. 



Behaviour of the Typhoid Bacillus and of the B. coli communis in 

 Steam-sterilised Thames Water (First Series of Experiments). 



It will now be interesting to consider the behaviour of these bacilli 

 in the precisely parallel series of experiments made with the same 

 sample of Thames water which had been previously sterilised by 

 steam. These experiments are of importance more especially because 

 they enable us to ascertain whether the water contains the necessary 

 food materials for these particular bacteria, as, owing to the absence 

 of other forms, it is now possible to determine how the actual numbers 

 of these bacteria are affected by residence in the water. 



The infection and distribution of these steam-sterilised waters has 

 already been described on pp. 410 and 411, so that I can pass at once to 

 their subsequent examination, made both by gelatine plate and phenol 

 broth-culture, at different intervals of time. 



In the table (p. 452) the fate of the typhoid bacilli introduced into 

 the steam-sterilised Thames water on 11.5.1893, is followed over a 

 period of seventy-six days, and it will be seen that during this time 

 their numbers underwent an almost continuous decline. Thus, whilst 

 at the outset they were present to the number of, in round numbers, 

 70,000 per cub. cm., at the end of this period their presence was 

 only just demonstrable by gelatine plate cultivation at all, and not 

 more than from 6 12 were discoverable in 1 cub. cm. The most 

 important feature in this chronicle of their deportment is the circum- 

 stance that they exhibited no multiplication or increase in numbers 

 during their residence in the water, clearly showing, therefore, that 

 the latter did not afford the nutriment and other conditions necessary 

 for the proliferation of the typhoid bacilli. In fact, the decline from 

 the commencement is an unbroken one, with the exception of the 

 solitary observation of an increase from 27,000 on 22.5.1893, to 42,000 

 on 29.5.1893, in the case of the water maintained at a winter tem- 

 perature. Whatever may have been the cause of this increase, it is 

 not sufficiently great to be comparable with that extensive reproduc- 

 tion which takes place in the case of those bacteria which are the 

 natural inhabitants of water. Moreover, that the water was not 

 suited to the well-being of the typhoid bacilli was further testified to 

 by the fact that the colonies on the gelatine plates became smaller, 

 feebler, and more degenerate as time went on, until on the occasion 

 of the last few examinations, they were, with difficulty, recognisable 

 a.s typhoid colonies, and exhibited a marked disinclination to form 

 the characteristic growths expanding over the surface of the gelatine. 



