Viruses 403 



are eliminated. Research has shown, however, that there is a 

 strong tendency for phage-resistant bacterial cells to develop, and 

 unless every cell is destroyed, the infection cannot be said to have 

 terminated. Injection of specific phage into such localized in- 

 fections as boils and carbuncles has been tried, but the results have 

 not warranted continued use of the practice. Injection and feed- 

 ing of large amounts of specific phage in cases of intestinal diseases 

 has met with similar disappointing results. 



VIRUS DISEASES OF PLANTS 

 In Bergey's tentative classification scheme the viruses affecting 

 plants are classed under the suborder Phytophagineae, and there 

 are six families listed according to the types of disease they cause 

 in plants. These families are: Chlorogenaceae (yellow diseases), 

 Marmoraceae (mosaics), Annulaceae (ringspots), Rugaceae (leaf- 

 curls), Savoiaceae (leaf-savoying), and Lethaceae ( spotted wilts ) . 

 Although the first virus disease ever described was that of tobacco 

 by Iwanowski in 1892, relatively little research was conducted on 

 plant diseases until about 1920. These diseases are of extreme 

 importance in agriculture, and methods for their control are essen- 

 tially parallel with those employed for combatting bacterial dis- 

 eases. By the use of various chemical sprays, insect populations 

 can be reduced, and since insects can serve as passive transfer 

 agents in virus as well as in bacterial diseases, insect vectors must 

 be controlled. Keeping healthy plants away from diseased plants 

 is another isolation control method. After handling diseased plants 

 it is imperative that tools and gloves be adequately disinfected 

 before handling non-diseased plants. The rotation of crops has 

 proved effective as a control measure in some areas with certain 

 plant diseases. 



VIRUS DISEASES OF ANIMALS 

 The Zoophagineae are members of the third suborder of viruses, 

 and six families are listed under this suborder. They are classified 

 as diseases in which insects are the exclusive hosts (Borrelinaceae), 



