SOIL AND SEWAGE 63 



vitality and their retention of virulence in such surroundings 

 is of great importance. This is particularly important in con- 

 nection with the contamination of water supplies. Although 

 numerous investigations have been made it cannot be said that 

 precise information on this subject is available. No doubt the 

 chemical composition and particularly the amount of organic 

 matter in the soil, as well as the number of other bacteria 

 present, play a very important part in the determination of the 

 length of life in soil of those pathogenic bacteria which are 

 not natural inhabitants of the soil. 



B. typhosus. A number of investigations have been carried 

 out by Sidney Martin, Firth and Horrocks, Rullmann, Dempster, 

 Pfuhl, Savage, Mair, and others, upon the vitality of typhoid 

 bacilli in soil. 



Of British investigators working with unsterilized soils 

 Robertson (1898) recovered the bacilli after 300 days, Martin 

 (1896-1901) could only recover the bacilli up to 12 days, Firth 

 and Horrocks (1902) found the bacilli to survive in some cases 

 up to 74 days, Lorrain Smith (1903) up to 21 days the average 

 being 15 days, Savage (1905), in polluted river mud treated 

 bi-weekly with fresh sea water, up to 5 weeks in one case and 

 fairly readily up to two weeks, and Mair (1908) in large numbers 

 for about 20 days and still present after 70 to 80 days. 



These results show considerable discrepancies. They show 

 that under favourable conditions the typhoid bacillus will survive 

 for a considerable period in soil, and that the factors influencing 

 its vitality are many and varied, the antagonism of other microbes 

 .and the physical conditions of moisture and temperature being 

 the most important. 



B. diphtheriae. This organism does not appear to have any 

 important relationship to soil, and there is no evidence that 

 infection has resulted from diphtheria bacilli derived from soil. 

 The absence of diphtheria outbreaks spread by water is evidence 

 in the same direction. But little experimental work has been 

 done upon the viability of the diphtheria bacillus in soils, 

 although Germano and others have shown that it may retain 

 its vitality in dust for some time. Leighton has shown that 



