240 C. p. RHOADS 



cally active elements. One argument against cancer as a mutation is the 

 "recognized irregularity of the chromosome equipment in cancer cells." 

 Whereas in given tumors no nuclear abnormality may be discernible, 

 other types present the appearance of extreme chromosome hetero- 

 geneity. 



Abnormal Growth due to Cell Free Materials 



The concept of cancer as a disease caused by a protein component of 

 cells, a "virus," has received increasing attention during the past few 

 years. Indeed, the point has been reached at which so much attention is 

 given to the filtrate or virus etiology as to obscure somewhat the exact 

 sense in which the term is used and its application to the possible pre- 

 vention or control of cancer. 



The original proof of cancer induction by a cellular component came 

 with the demonstration by Rous (89) that a malignant mesoblastic 

 tumor of fowls, occurring spontaneously, could be transmitted to nor- 

 mal birds by the inoculation of cell-free antigenic material from the 

 original growth. Subsequent studies by Claude revealed that the active 

 material is a complex composed of lipo-protein and a ribose nucleic 

 acid, and that it is chemically and immunologically indistinguishable 

 from certain constituents of normal embryonic fowl cells. The con- 

 clusiveness of the evidence suggested that other, indeed perhaps all, 

 neoplasms are due to cell-free agents and that cancer in general is an 

 infectious contagious disease. This inclusive and far-reaching view was 

 supported by the fact that a number of other fowl tumors were proved 

 to be capable of being transmitted by cell-free material. Particularly 

 striking is the evidence of Ellermann (91) concerning fowl leukosis. 

 This neoplasm not only can be transmitted by filtrates but also appears 

 to be truly contagious, since contact transmission seems to have been 

 proven completely by the distinguished work of the Michigan investiga- 

 tors (92). Later studies revealed a number of additional examples of 

 active tumor-producing cell-free materials. The Shope papilloma of cot- 

 tontail rabbits, the oral papilloma of dogs, and the mammary tumor 

 inciter of mice are all agents which may be dissociated from whole cells 

 and which certainly cause benign neoplasms to appear. 



The studies of Berry (93) are important in any consideration of the 

 virus etiology of neoplastic disease. This investigator used the principles 

 effective in demonstrating the transforming principle of pneumococci 

 in the transformation of the virus of rabbit fibromatosis to an agent 



