164 ANTAGONISMS BETWEEN NONSPECIFIC PATHOGENS 



inactivates plant viruses and is not detrimental to most forms of life. 

 Various microorganisms are capable of producing such inactivators. 

 Plant viruses differ in their sensitivity to "nontoxic" inactivators. Ac- 

 cording to Johnson (473) various microorganisms are capable of form- 

 ing such inactivators against tobacco-mosaic virus. The inactivators pro- 

 duced by A. aero genes and A. niger are particularly effective against a 

 variety of plant viruses, but not against all of themj the inactivators 

 produced by the two organisms appear to be similar. They are com- 

 paratively heat stable but are slowly destroyed by certain organisms. 

 They can be concentrated by evaporation of medium. A substance 

 which was capable of rapidly inactivating the tobacco-mosaic virus was 

 isolated (895) from yeast. A chemical reaction between the inactivating 

 principle and the virus was therefore suggested. The inactivator in this 

 instance was destroyed by heating with i TV NaOH solution, but not by 

 2 N HCl. It was not a protein and gave on analysis 39.7 per cent C and 

 5.85 per cent H. The substance was said to be a polysaccharide. A. niger 

 was also found (307) to form in the medium a substance capable of in- 

 activating a number of different plant viruses; the effect of the inactiva- 

 tor was found to be exerted upon the virus itself and not upon the plant. 

 Of 150 organisms, comprising bacteria, fungi, and actinomycetes, 

 isolated from different natural substrates as well as from soil enriched 

 with virus concentrates, only three showed some inactivation of the 

 fowl pox virus, and, in one case, of the laryngotracheitis virus. The 

 active principle of one of these organisms was actinomycin, an anti- 

 bacterial substance known to be highly toxic to animals (477). 



ANTIBIOTIC SUBSTANCES, VIRUSES, AND 

 PHAGES 



The first recorded observation on the effect of antibiotics upon vi- 

 ruses is that of Fukuhara (304) who demonstrated that pyocyanase, 

 after having been in contact with the viruses of vaccinia, rabies, and 

 chicken pest, brought about their inactivation, as shown by the fact 

 that when viruses so treated were inoculated into experimental animals 

 the respective diseases did not develop. 



Most of the viruses, however, appear to be resistant to the action of 



