334 H. B. ANDERVONT 



of the amount of virus necessary to provoke lesions in most susceptible 

 rabbits and a comparison of these calculations with the amounts of virus 

 recoverable from domestic rabbits indicated there was an insufficient 

 quantity of virus in papillomas of domestic rabbits to induce growths in new 

 hosts. Thus, the noninfectiousness of material from papillomas of domestic 

 rabbits reflected the small quantity of virus they contained, and was not 

 related to a change in the quality of the virus. He exposed the weakness of 

 serological studies interpreted as bolstering the theory of masked virus, by 

 computing the amount of purified virus necessary for the production of 

 antibodies and showing that, in the domestic rabbit, this quantity was 

 considerably less than the amount required to induce papillomas. 



The reader must read Beard's publication to judge for himself the validity 

 of the evidence. Beard may be open to the criticism that his conclusions 

 concerning the infectiousness of the virus include only the infective stage of 

 the virus, but his use of serological studies to refute the theory is challenging. 

 Kegardless of the final outcome of the controversy, Beard has established the 

 point that the acquisition of purified virus preparations and the use of such 

 materials in quantitative studies of the host-virus relationships are essential 

 before a qualitative change in the virus is accepted as the causation of 

 unexplained findings. Finally, he focused attention uporj the host and stated: 

 "The influence of the genetic status of the host, with respect to the individual, 

 to the strain, and to the species, on tumor virus infection and multiplication 

 can scarcely be overemphasized." 



It is safe to assume that further investigations with this virus concerning 

 the "masking" phenomenon will contribute to the knowledge of tumor 

 viruses. Tissue cultures of papilloma and carcinoma cells could be compared 

 for the presence of virus, and the ability of the virus to transform normal or 

 papilloma cells to malignant cells in vitro could be explored. Other avenues of 

 approach are open and these will certainly be pursued because of the recent 

 interest in the viral etiology of tumors. 



Before closing this discussion, it is deemed necessary to mention two other 

 major contributions to the tumor problem resulting from work with this 

 virus. These have been overlooked because of the position the virus holds in 

 the dispute over the "masking" phenomenon. The papilloma virus was the 

 first tumor virus to be purified. Its presence in large quantities in keratinized 

 papilloma cells of cottontail rabbits simplified the problem of isolation 

 (Beard et at., 1939). Of more interest to the problems of the tumor viruses was 

 the use of the virus for first studies of host- virus relationships in which 

 biomathematical procedures were used (Bryan and Beard, 1939, 1940a,b,c). 

 The application of newer analytical methods to the tumor viruses has done 

 much to extend knowledge of the properties of the viruses and to clarify the 

 problems of host-virus and cell-virus interactions. 



