98 F. B. BANG 



number of particles seen in sections of tumors and the infectiousness of the 

 tumor extract has recently been completed (Hagenau et ah, 1958). In this 

 study the more infectious tumors showed the greatest number of character- 

 istic particles, and the pellets obtained from highly infectious extracts 

 showed many more particles than those of low infectiousness. It is clear that 

 a beginning in the identification has been made. However, the immuno- 

 logical tests, purification, spray droplet correlations, etc., which may con- 

 clusively establish these particles as the agents of infection have not been 

 completed. Confirmation is especially important. A small percentage of 

 normal chick embryo tissue cultures yield preparations with large numbers 

 of identical particles (Bang, 1954; Gey and Bang, 1951). 



Further complications are added when related tumors, such as the Murray - 

 Begg endothelioma (Rouiller et al., 1956) and leukemias (Benedetti et al., 

 1956), are studied for both of these have similar particles. In the latter, 3 of 

 24 spleens from "normal" chickens showed the same particles. The morpho- 

 logical difficulties have then emphasized the fact that most stocks of chickens 

 acquire antibodies to these agents (Andrewes, 1939; Bang and Haley, 1958), 

 and that uncontaminated control animals are difficult to obtain. It is tempt- 

 ing to explain these contradictions by supposing that virus tumor cells carry 

 the virus in a latent lysogenic state, and that the infectious and visible form 

 of the virus is important in producing what may well be secondary patho- 

 logical changes in infected cells, whereas the really malignant cell does not 

 necessarily carry the virus in this form. The recognition that the disturbed 

 cell is one in which host cell and virus are not in balance, whereas the trans- 

 missible tumor cell is in balance with its virus would support this idea (Bang, 

 1955a). 



3. Localization of Virus 



In all of the above studies on the Rous sarcoma the viruses have been 

 found predominantly at the surface of the cell or within vacuoles which are 

 in a way not in contact with the cell. It is, therefore, not easy to perceive the 

 method of formation of the complete virus. In a few cases particles have 

 aggregated within vesicles which could well be altered mitochondria. 



The possibility that the characteristic virus particle, which is assumed to 

 be the infectious unit, represents only a terminal phase of the partnership 

 which is the tumor cell, focuses particular interest on the morphology of the 

 tumor cell. Early observations on this are presented in the beginning of this 

 chapter. Recent electron microscope studies of the "fibroblast-like tumor 

 cells of Rous sarcomata" (Epstein, 1957) show that the infrastructure of these 

 cells is similar to that of other cells and fails to bring out any qualitative 

 morphological difference between normal fibroblasts and the tumor cells. 

 Attention was, however, directed upon the tightly packed piles of smooth 



