122 ACTINOMYCETES AS ANTAGONISTS 



bing on the test potatoes was reduced from lOO per cent to nil. The 

 sterilized soil provided sufficient nutrients for the development of the 

 antagonist and only a small increase in the control was obtained when 

 grass cuttings were added and sterilized along with the soil. 



Sanford (782) was unable, however, to control potato scab by the 

 inoculation, with S. scabies and S. -praecoXy of both steam-sterilized and 

 natural soil containing different amounts of green plant materials. 

 These organisms were perfectly compatible on potato dextrose agar, as 

 well as in a steam-sterilized soil medium. The control of scab (605), 

 therefore, was said to have been due not to the direct action of S. fraecox 

 but to certain other undetermined microorganisms favored by the pres- 

 ence of the green manure. S. scabies was found (782) to be very sensi- 

 tive to various products of fungi and bacteria. When grown in close 

 proximity to various bacteria, the acid production of the latter inhibited 

 S. scabies to a considerable degree. Its complete inhibition was not due 

 to the acid reaction alone, however, since a certain bacterium was iso- 

 lated from the soil which definitely inhibited the growth of this plant 

 pathogen. 



Goss (342) observed that the severity of scab is dependent on the 

 amount of S. scabies present in the soil, which was believed to be con- 

 trolled by the soil microflora. No evidence was obtained as to whether 

 the effect of the soil flora on S. scabies was due to specific organisms. 

 Kieszling (481 ) isolated two cultures of bacteria which were antagonis- 

 tic to S. scabies; when added to the soil, these bacteria prevented the 

 development of scab on potatoes. 



The ability of antibiotic substances produced by actinomycetes to 

 exert a marked inhibiting effect upon plant pathogenic bacteria has been 

 established (930). 



IN VIVO ACTIVITY OF SUBSTANCES PRODUCED 

 BY ACTINOMYCETES 



Just as the chemical nature of the antibiotic agents produced by ac- 

 tinomycetes varies, so does the action of these agents in the animal body. 

 Some, like actinomycin, are very toxic, whereas others, like streptothri- 

 cin and streptomycin, have low toxicity and give great promise of prac- 



