THE GENETICS OF SPONTANEOUS TUMOR FORMATION 267 



high and low tumor strains that are extensive enough in the first hybrid (Fi) 

 generations to give significant results. 



Table 14 

 Types of Non-epithelial Tumors in the C57 Black Stock 



It is necessary, therefore, to compare the F2 hybrids formed from a 

 reciprocal cross between two inbred strains. While the two strains are not 



Table 15 

 Distrlbution by Site of 121 Tumors in the C57 Black Stock 



classifiable with complete accuracy as "high" and "low," there does seem to 

 be a difference between them so that we can tentatively classify the dilute 

 brown (dba) strain as "lower" in incidence of non-epithelial tumors and the 



