24 ELEMENTS OF WATER BACTERIOLOGY 



viability for the typhoid bacillus. Savage (1905) 

 added a heavy dose of the organism to unsterilized 

 tidal mud and found it living after 5 weeks. Hoffmann 

 (1905), after inoculating a large aquarium with a rich 

 typhoid culture, was able to isolate the germ from the 

 water after four weeks and from the mud at the bottom 

 after two months. Konradi (1904) reports the per- 

 sistence of typhoid bacilli in unsterilized tap water 

 for over a year. 



These last experiments deal only with the maximum 

 survival period for a few out of great numbers of germs 

 introduced into the water or mud, and entirely ignore 

 the quantitative aspects of the case. When one con- 

 siders the proportion of the original bacteria surviving, 

 the period necessary to bring about a reasonably safe 

 condition is found to be much shorter. Houston 

 (1908) has shown that when water is artificially infected 

 with .typhoid bacilli and stored, 99.9 per cent of the 

 disease germs perish in one week, although some may 

 persist for from i to 9 weeks. 



In later experiments (Houston, 1911) he finds that 

 " uncultivated " typhoid bacilli added to the water 

 directly from the urinary sediment of a disease carrier 

 perish much more rapidly than the laboratory strains, 

 usually disappearing entirely after one week and always 

 after three. On a number of occasions Dr. Houston 

 gave dramatic expression to his confidence in these 

 negative laboratory findings by drinking half pint 

 portions of water which a few weeks previously had 

 contained millions of typhoid bacilli. We have plenty 

 of practical epidemiological evidence, such as that 



