406 



Profs. Percy Frankland and Marshall Ward. 



which has been affirmed more especially by Kraus and subsequently 

 by Karlinski. This point is obviously of the very highest import- 

 ance from a practical hygienic point of view, as it is with unsterile 

 potable water that we are in practice alone concerned, and the 

 duration of vitality ascribed to the typhoid bacillus in such water by 

 both these observers is of very limited extent not more than seven 

 days. 



The experiments of Kraus are so striking, and have attracted so 

 much attention, that I will give them in more detail in the following 

 table : 



Typhoid Bacillus. 



These results indicate, therefore, that, on introducing the typhoid 

 bacilli into the potable waters in question, which were almost 

 naturally sterile, the typhoid bacilli promptly disappeared as soon as 

 the water bacteria had undergone extensive multiplication, which 

 had taken place in each of the three experiments by the seventh day 

 after the importation of the typhoid bacilli. 



These interesting experiments cannot, however, by the light of our 

 present knowledge, be accepted without criticism, for there cannot 

 be the slightest doubt that, when only the ordinary method of plate- 

 cultivation is employed in such investigations on unsterilised water, 

 the typhoid bacilli will be generally overlooked unless they are 

 present in large numbers. Again, the attempts which have been 

 made, both by Kraus and other experimenters, to count the typhoid 

 colonies on plates containing such mixtures of colonies, and the 

 numerical estimates given of the typhoid bacilli in such unsterilised 

 waters, must be wholly illusory, for the number of typhoid colonies 

 which develope what may be called a typical appearance (i.e., one 

 which enables them to be readily recognised with reasonable cer- 

 tainty) depends on a variety of different circumstances, amongst 

 which may be mentioned the age of the plate, the extent to which 



