SURVIVAL OF PATHOGENS IN SOIL AND WATER 29 



these organisms received particular attention during the first world 

 war, which was fought chiefly in trenches (957). 



Another important pathogenic anaerobe able to survive in soil for 

 long periods of time is Clostridium chauvoeiy the causative agent of 

 blackleg in cattle j southern pastures are said to be better carriers of 

 blackleg than northern pastures. 



Clostridium tetani is also widely distributed in the soil and appears to 

 be associated with the use of stable manures, Nicolaier (638, 639) 

 found, in 1884, that tetanus could be produced in experimental animals 

 by the injection of soil samples, 69 positive results being obtained from 

 140 inoculations. This organism is believed to occur in the soil in the 

 form of spores ; its mode of survival, however, is not sufficiently known 

 because of a lack of careful study. 



The botulinus organism not only may remain alive in the soil for a 

 long time (602), but it may also produce there a potent toxin that 

 causes much loss of water fowl and other wild life. Aeration of the soil 

 results in the destruction of this toxin by aerobic bacteria (710), 



Thus we see that pathogenic spore-forming bacteria are always found 

 in the soil. Other pathogens are able to survive in the soil only for lim- 

 ited periods of time. They are eliminated sooner or later from the soil, 

 either because of their inability to compete with the soil population or 

 because of their actual destruction by the latter. Although the patho- 

 gens seem to possess considerable resistance toward unfavorable soil con- 

 ditions, they are unable to multiply at rates permitting their indefinite 

 survival in the soiL The anthrax bacillus and certain other parasites in- 

 festing domesticated and wild animals belong to this group. Certain in- 

 sect and animal carriers make possible the survival and spread of many 

 pathogens in the soil. 



Organisms that Survive for Brief Periods 



The great majority of disease-producing bacteria, however, are able 

 to survive only for very brief periods outside their respective hosts, 

 especially in soil and water. It is sufficient to cite the fact that typhoid 

 and dysentery bacteria, which are known to contaminate watersheds 

 and water supplies, disappear sooner or later. It has been estimated, for 



