GROWTH OF A TRANSPLANTABLE TUMOR IN MICE os 
contrasted. The upper group shows 10.30+1.20 per cent of 
growth, while the lower group shows 15.70+1.64 per cent. The 
difference is 2.6 times its probable error and, while considerable, 
cannot be regarded as significant. 
The females, however, show a significant distinction between 
the two age groups. The upper age group has a growth per- 
centage of 9.39-+0.87, and the lower group one of 19.46+1.31. 
The difference between them is 10.71.51, or seven times its 
probable error. There is, then, clear evidence that the females 
are distinctly more tolerant to the growth of the tumor when 
they are inoculated at an extremely early age than when they 
are inoculated a little later on. The significance of this fact 
will be discussed later. 
TABLE 7 
BACK-CROSS O'S 
+ - % + 
DEO ee 2) erry. 36 212 14.51+1.51 || Diff. 0.87+2.16 
RPA 5 SY ots 2 38 209 15.3881.55 | J 0.4 < P.E. 
BaCK-CROSS Q'S 
6 |\ Diff. 13.62+2.71 
7 5 Pa. 
In the (B.C.) series, the males show approximately the same 
amount of records showing growth as do the males of the (N) 
series. The actual figures are 14.94+1.09 as compared with 
13.17 in the (N) series. The contrast between the age groups is 
even less marked than in series (N). The percentage in the higher 
group is 15.38+1.55, and in the lower group 14.51+1.51. There 
is, then, no difference between the age groups as regards the per- 
centage of observations showing tumor growth. The females 
are, however, again strikingly different and, what is even more 
interesting, show a departure from one another and from the 
males in quite the opposite direction from that taken by the 
females of the (N) series. Thus the lower age group of the 
(B.C.) series females shows a percentage of 12.12+1.76, a value 
