28 



NATURE, FORMATION, AND ACTIVITIES 



plied to the overlay culture 1 hour after 

 virus infection; large plaque-free areas re- 

 sulted when 100 yug were applied 46 hours 

 after \'irus infection. 



Certain glycoproteins in the sap of various 

 plants were found capable of reducing the 

 infecti\nty of several plant viruses. On 

 dilution, however, noninfective mixtures re- 

 gained infectivity, thus indicating a lack of 

 combining ratio between virus and inhibitor 

 necessary to cause a loss of infectivity 

 (Kassanis and Kleczkowski, 1948). It has 

 been suggested, howe\'er, that the evidence 

 points not to a combination effect of virus 

 and proteins, but rather to the effect of the 

 latter upon the host, or to an antagonistic 

 behavior between the virus and inhibitor. 

 Among the inhibiting factors, the action of 

 ribonuclease on ribonucleic acid viruses is of 

 particular interest. This enzyme hydrolyzes 

 the nucleic acid deri\'ed from these viruses, 

 but seems to have no effect upon the intact 

 viruses. When mixed with the ^'irus, how- 

 ever, the enzyme combines with it and in- 

 hibits its infectivity re\'ersibly in a manner 

 similar to protein (Bawden and Pirie, 1957). 

 Other substances capable of inhibiting the 

 infectivity of plant viruses include certain 

 yeast polysaccharides (Kleczkowski, 1946). 



Table (5 

 Effect of a nocardia antibiotic on tobacco mosaic 

 virus multiplication under different light in- 

 tensities (Schlegel and Rawlins, 1954) 



Some of these substances, like primycin, 

 exert not only antiA'iral but also antibac- 

 terial effects; some were foimd able to cause 

 marked destruction of worms. These sub- 

 stances vary in s()lu!)ility, stability, activity, 

 and toxicity. 



Schlegel and Rawlins (1904) isolated from 

 a Nocardia a substance found to be efTective 

 in inhibiting multiplication of tobacco 

 mosaic virus in floating leaf discs. Its action 

 appeared to be relatively independent of 

 changes in host composition produced by 

 light. It was concluded that it inhibits virus 

 increase by acting directly upon virus 

 multiplication rather than on host metab- 

 olism (Table 6). Other antiviral agents 

 produced by Nocardia have been studied by 

 Harris and Woodruff (1953). Kuroya et al. 

 (1957) examined 418 culture filtrates of 

 freshly isolated streptomycetes for their 

 activity against influenza virus cultivated 

 in vitro. Of the filtrates 21.5 per cent showed 

 some activity. There was no correlation be- 

 tween activity and any other biological 

 properties of the organism. 



Unfortunately, none of these numerous 

 preparations can be said to have a suf- 

 ficiently suppressive effect upon viral 

 diseases to warrant use in chemotherapy of 

 such diseases. In analyzing the failure to 

 obtain antiviral substances of practical 

 significance, Waksman (19()0) concluded 

 that since viruses do not grow and do not 

 metabolize, the whole approach to their 

 suppression must be different from that of 

 antibiotics which act upon the living systems 

 of bacteria, fungi, and other microorganisms. 



Further observations on anti\'iral agents 

 and reasons for failure to obtain good 

 preparations ha^'e been examined by Leva- 

 diti (1952), Kuroya ct al. (1957), Krassilni- 

 kov d al. (1960), and Waksman (1960). 



.1 ntitrichomonal A gents 



Yamaguchi and Sabiu'i (1955) found that 

 of 1244 cultures of actinomycetes, 172 pos- 

 sessed antitrichomonal properties; a few of 



