NEOPLASTIC ABNORMAL GROWTH 243 



The presence of the inhibitor in tumor is invoked to explain the in- 

 ability to recover virus from mixed papillomas and cancers of cotton- 

 tails, as well as from the cancer tissue alone. Friedewald (loi) reported 

 that antibody to the papilloma virus is present in extracts of the virus- 

 induced growths of domestic rabbits, even though little or none may be 

 present in the serum. This fact is used to explain the failure to obtain 

 virus from the papillomas and also to explain, as due to extravasated 

 antibody, the presence of inhibitor in the cancer in the cottontail arising 

 in the virus-induced papilloma, a view in support of which morpholog- 

 ical evidence of hemorrhage and extravasation is advanced. 



Since no way was thought feasible of separating extravasated anti- 

 body from the papilloma virus and so of demonstrating the masked 

 virus in the cancer derived from the papilloma of the cottontail, an ex- 

 periment was made to recover virus from a cancer not caused by it, and 

 so not productive of antibody (looa). Virus was mixed with the tissue 

 of tar-induced cancer of cottontails and the tissue transplanted into nor- 

 mal hosts. Antibodies to the virus were developed and the virus is stated 

 to have increased the speed of growth of the implanted tumors and 

 sometimes to have altered their morphology so that they looked, not 

 like tar cancers, but like virus cancers. From these transplanted virus- 

 infected tar cancers virus could sometimes be recovered if the anti-viral 

 activity of the host's blood had not risen to levels too high to allow a 

 satisfactory test. It is not clear how virus escapes from the cells bearing 

 it to act as an antigen, but the antibody fails to penetrate the cells and 

 kill the virus. 



Whereas the papilloma caused by virus inoculation in the cottontail 

 yields virus regularly on test and is associated with virus-neutralizing 

 humoral antibodies, in domestic rabbits from flourishing papillomas 

 caused by the same material virus was obtained only irregularly. Fur- 

 thermore, the sera of the animals that carried growths yielding little or 

 no virus had little or no virus-neutralizing capacity. These findings are 

 summed up by the statement that the facts make it improbable that anti- 

 body is responsible for masking the virus in the growths produced by it 

 in domestic rabbits, although the presence of antibody as inhibitor in 

 tumor tissue is invoked to explain the inability to recover virus from the 

 inflamed papilloma cancers of cottontails. 



It is remarkable that no antibodies can be shown to be associated with 

 the papilloma, which yields no virus but gives rise to a cancer also not 

 yielding virus but actively productive of antibody. Antibody cannot ex- 

 plain the failure to obtain virus from papilloma of domestic rabbits but 



