286 



Disease-Producing Microorganisms 



doubt, however, that some aerobic actinomycetes are capable of 

 causing infections of men and animals. 



The hookworm disease, caused by Ancijlosfoma duodenale and 

 Necator americamis, is primarily due to soil pollution. The larvae 

 were found to develop for as long as 6 months in soil protected by 



— 2 



12 



10 



7.0 



Fig. 113. Relation of soil reaction to the growth of scab organism and occur- 

 rence of potato scab (from Dippenaar). 



vegetation. The physical, chemical, and biological soil conditions 

 have a very important influence upon the development of hookworm 

 larvae from infected feces and upon the continued life of these larvae 

 in the soil. The larvae are found largely in the capillary film of mois- 

 ture surrounding the soil particles. 



In spite of the gradual and even rapid destruction of some patho- 

 genic microorganisms in the soil, the survival of others presents im- 

 portant problems to farmers raising hogs, cattle, poultry, and other 

 domestic animals. To overcome this condition, rotation of crops is 

 usually practiced; several years are generally required to render 



