36 HUMAN AND ANIMAL WASTES 



in manured soil. In nonsterile soil, the pathogen was slowly destroyed, 

 the plate count being reduced to about one sixth of the original in 

 I month. In a study of the survival of avian tubercle bacteria in sewage 

 and in stream water, there was a reduction, in 73 days, from 48,000 to 

 1,400 per milliliter in sewage and to 4,200 in water (745). 



Other Disease-froducing Microor ganisms 



A study of the viability of Brucella melltensls in soil and in water in 

 Malta brought out the fact that the organism survived in sterile tap 

 water 42 days and in unsterile tap water only 7 days. It survived 25 

 days in soil and 69 days in dry sterile soil, but only 20 days in unsterile 

 manured soil, 28 days in dry natural road dust, 20 days in dry sterile 

 sand, and 80 days on dry cloth (326, 430, 431, 432). 



The rapid destruction of cholera bacteria added to soil was first 

 pointed out by Houston (437). Similar rapid destruction of the diph- 

 theria organism was also noted. Serratia, however, retained its vitality 

 for 158 days. Vibrio comma also survived for a short time only in feces 

 (358), different strains showing considerable variability; temperature 

 was an important factor. During the hot season in Calcutta, the viable 

 period was somewhat longer than a day, as compared to 7 or 8 days 

 during the cold season ; the critical cholera months were found to fol- 

 low directly the cool months. The organism did not survive very long 

 in fresh water, although the time appeared to be long enough to cause 

 occasional serious epidemics. It remained alive for 47 days in sea water 

 (450). The conclusion was reached that although the organism is ordi- 

 narily destroyed rapidly in water as a result of competition with other 

 microbes, it may survive in certain instances for some time. 



THE SOIL POPULATION 



The nature of the soil population can thus be considered as more or 

 less dynamic, its modification being controlled by the addition of or- 

 ganic matter and by soil treatments. The introduction of foreign organ- 

 isms tends not to change the nature of the population, but merely to 

 stimulate the development of such members as are capable of destroying 

 the foreign organisms. The production of antibiotic substances by mem- 



