16 MICROORGANISMS IN SOILS AND WATER BASINS 



capable of growing in heated soil. This was found to be due to the fact 

 that normal soils contain certain substances that render the growth of 

 the fungus impossible j these substances are destroyed by heating. An 

 extract of fresh soil acts injuriously upon the growth of the fungus 

 Pyronema; the injurious effect is partly removed on boiling. Certain 

 forest soils contain not only antifungal but also antibacterial factors 

 (630a) which are dialyzable and thermostable j other thermolabile and 

 nonfilterable substances may be present which neutralize the effect of 

 the antibiotics. 



The survival of microorganisms added to soil or water is thus influ- 

 enced by the nature of the native soil or water population, the organ- 

 isms added, the composition of the substrate, and various environ- 

 mental conditions. 



SAPROPHYTIC AND PATHOGENIC NATURE OF 

 CERTAIN SOIL MICROORGANISMS 



Various fungi and actinomycetes causing animal diseases, notably 

 skin infections, appear to resemble very closely the corresponding soil 

 saprophytes. It was therefore suggested that many of the dermato- 

 phytic fungi normally lead a saprophytic existence in the soil but are 

 also capable of developing on epidermal tissue and bringing about in- 

 fection of the tissues. This was found to be true especially of species of 

 S-porotrkhum, various actinomycetes such as those causing lumpy jaw of 

 cattle, and certain other organisms. Henrici (406) divided fungus in- 

 fections of animals into two groups : first, superficial mycoses, compris- 

 ing moniliases and dermatomycoses, that are caused by a variety of 

 fungi widely distributed in nature 5 and, second, deep-seated infections, 

 namely, aspergillosis, sporotrichosis, and blastomycosis, with a marked 

 tendency to restricted distribution. The latter were said to be caused 

 primarily by saprophytic forms, including varieties capable of chance 

 survival and of multiplication when accidentally introduced into ani- 

 mal tissues. 



Walker (981) suggested that the partly acid-fast coccoid, diph- 

 theroid, and actinomycoid organisms that have been cultivated repeat- 

 edly from leprosy are merely different stages in the life cycle of the 



