PKOBLEMS CONCERNING THE TUMOR VIRUSES 355 



tumor of the adrenal medulla was a "good source of parotid-gland tumor- 

 inducing substance." In a later paper, Law (1957) recorded the occurrence of 

 6 spontaneous cases of parotid tumors in about 200 untreated C3H/Fg mice 

 and, in one family of C3H mice obtained from Bittner, 5 spontaneous cases in a 

 total of 70 mice. These latter tumors were in mice of the same substrain as those 

 in which Gross found but one such spontaneous tumor in his total experience. 



Perhaps Law's most important observation was the tendency of the parotid 

 tumors to appear in certain litters, because there must be a reason for a 

 distribution of this kind within an inbred strain. Law et al. (1955) procured 

 31 offspring from C3H females which had parotid tumors during the nursing 

 period, but none of the offspring developed a similar tumor. It would be of 

 much interest to know whether the parotid tumors in Gross' experiments 

 were also confined to certain litters. Gross (1955b) stated that the first parotid 

 tumor to appear in his mice was found on November 9, 1951, and within 

 "a week or two" 2 additional mice in the same litter developed the same 

 type of tumor. 



Woolley and Small (1956) obtained parotid tumors in C3H mice which had 

 been inoculated with centrifuged and filtered extracts of AK/n leukemias,but 

 no mention was made of litter distribution. In a later paper, Woolley and 

 Small (1957) included 11 parotid tumors appearing in C3H mice following 

 administration of cell-free leukemic extracts, but failed to mention litter 

 distribution, although they recorded that 4 mice bearing cortisone-induced 

 parotid tumors were not litter mates. This paper is of particular significance 

 because it contained a summation of Woolley's experiments in which he 

 produced parotid tumors in mice exposed to chronic administration of 

 cortisone. Of the high-leukemia strains used, strain AKR mice failed to 

 develop parotid tumors, while 3.5 % of the C58 strain and 8.0 % of hybrids 

 derived from C58 females and AKR males did so. Of the low-leukemia strains 

 used, 9.3 % of the C3H Gross subline developed parotid tumors whereas none 

 of the C3H Hummel subline (related to the NCI substrain) did so. They 

 thought the results in these C3H mice suggested a substrain difference in 

 response to cortisone. Of much more importance to the subject under discus- 

 sion is the opportunity it gives investigators to test for the presence of agents 

 in the parotid tumors. These tumors, those arising spontaneously in Law's 

 mice, and the one described by Gross are the only parotid tumors found, 

 thus far, in strain C3H mice which had not received materials from tissue 

 extracts, and it is of utmost importance that cell-free extracts from such 

 growths be examined for tumor-inducing agents. This could be an excellent 

 approach to the problem of the relationship between the leukemia and 

 parotid tumor viruses. 



Dulaney (1956) reported that cell-free extracts prepared from AKR or 

 AK/n leukemias produced parotid tumors in strain AKR mice and that the 



