a2 C2) °C LITTLE 
EXPERIMENTAL 
Table 1 shows the observations taken on albino stock mice. 
In this and in subsequent tabulations, the sign plus stands for 
records showing a mass, and the sign minus stands for records 
showing no growth. It will be seen that the grand total of ob- 
servations is 233 plus to 1862 minus. In other words, 11.12 
per cent +0.46 of the observations show growth of the tumor. 
Table 2 shows a similar treatment of the back-cross generation 
in which a total of 170 plus to 799 minus have been obtained. 
TABLE 1! 
Common stock (N) 
2 WEEKS 3 WEEKS | 4 WEEKS | 5 WEEKS | 6 WEEKS TOTAL 
AGE 70 ar 
+/—-}+]/-;4+]-}4+]-]4]-] 4+] - 
20. 40} 1 40) 3 | 37) 3) 24) 1 | 21 9) 162 03 
18 1D 24 4) Baa | 29 sO es2) TOMI 24). 20) 141 12.4 
16 BH AS Sy aay, ae |] Sul ay |) AoW A tsi Kay ess 99 
14 12 54| 8 57| 9 | 56) 5} 55) 2) 58) 36; 280) 11.4 
(4 5), OLP oa) 86) on oll oon Le Sait 19) s226 8.1 
10 9 |. 29)-.5 |. 238) iGo) 31) 2.) 271 0, |. 20) 22) 29130 1 145 
8 a 15) 3 19} 3 19] 2 14) 2 14 7 17.3 
6° 7 | 58) 14 50} 5 | 57) 4) 47) 4] 47) 34) 259) 15.0 
4 12 | 62} 10] 62) 5] 65) 4) 66) 3] 66) 34 321 9.8 
2 FN 29) PREZ Wh 22) ae 22 aa! S231 2G ee 18.1 
75 | 391] 60 | 371] 48 | 398} 31 | 364! 19 | 338) 233) 1862 | 11.12+0.46 
This is a percentage of 17.54+0.83 showing tumor growth. As 
the tables show, these totals lump all ages and all observations 
on both sexes. It will be seen that the difference between the 
series is 6.7 times its probable error and is therefore certainly 
significant. Since there is such a difference and since we know 
that in all probability the back-cross generation animals possess 
hereditary factors favoring tumor growth which are absent from 
the albino stock it will be of interest to analyze the data further in 
an attempt to locate more accurately certain of these factors 
and to determine, if possible, something of their physiological 
nature. 
