Report on the Bacteriology of Water. 541 



Another experiment was made on similar lines to the first half of 

 the above experiment, to see whether the multiplication there observed 

 could be confirmed, thus : 



On 27.3.1894, 4 c.c. of a 1 per cent, broth cultivation (three 

 days old) of the typhoid bacillus were put into 50 c.c. of steam- 

 sterilised Thames water, the mixture being violently shaken up for 

 fifteen minutes ; 2 c.c. of this mixture (equivalent to -$ T c.c. of the 

 original 1 per cent, broth culture) were then added to 200 c.c. of 

 steam-sterilised Thames water, which was then submitted to plate 

 cultivation as follows : 



Number of days 



Dates on which plates plates -were Number of typhoid bacilli 



were prepared. incubated. in 1 c.c. of water. 



27.3.1894 6 37,515 



29.3.1894 6 61,566 



31.3.1894 9 50,935 



4.4.1894 6 27,818 



11.4.1894 8 20,130 



In this case again, therefore, there was a smalt but distinct multi- 

 plication. 



From these experiments it appears that typhoid bacilli ivhich have 

 undergone a prolonged and gradual training in more and more aqueous 

 culture-media do exhibit distinctly more vitality in potable ivater than 

 bacilli which are at once transferred into icater from highly nutritive 

 solid media like agar or peptone jelly. On the other hand, there is con- 

 siderable reason for believing that the slight but distinct multiplication 

 which these trained bacilli undergo in potable water, is effected at the 

 expense of small quantities of food-material introduced along with them, 

 at the time of infection, and not at the expense of the organic matter 

 belonging to the water itself. 



The result of the experiments with these specially-trained typhoid 

 bacilli greatly fortifies the opinion which I have expressed above, that 

 the extensive multiplication of typhoid bacilli in potable waters which 

 has been observed by some investigators was most probably due to 

 the importation of appreciable quantities of food-material along with 

 the bacilli themselves. 



SUMMARY. 



The investigation which has been detailed in the foregoing pages 

 is divisible into the following sections : 



1. A series of experiments in which the vitality of one and the 

 same culture of the typhoid bacillus was observed in one and 

 the same sample of Thames water, using the latter under 

 the following conditions : 



2 o 2 



