324 Cc. Cc. LITTLE 
of the Japanese mouse factors they possess, thus favoring at least 
temporary growth of the tumor implant. 
If this is the correct explanation, the difference between upper 
and lower age groups in the (B.C.) generation should be more 
marked in females ‘than in males. Furthermore, the females 
should show a distinctly higher percentage of growth in the upper 
age group than in the lower. Table 7 shows this to be actually 
the case. The upper group females show 25.74+2.07 per cent 
erowth, while the lower group females show 12.12+1.76. The 
difference is five times its probable error. The males, on the 
other hand, show no significant difference between upper and 
lower groups and a total growth percentage of 14.94+1.09. 
Leaving the genetic analysis of the difference between the 
Japanese factor complex and that of the common non-waltzing 
mice to be treated in another communication, now in press, we 
may on the basis of the data given here conclude that: 
1. Animals of a race non-susceptible to inoculation with bits 
of a sarcoma (J.W.B.) derived from a closely inbred race of 
Japanese waltzing mice, show temporary growth of the tumor in 
11.12+0.46 per cent of the 2095 observations made. 
2. The percentage of observations showing growth decreases 
steadily on successive weeks (second to sixth, inclusive) after 
inoculation (fig. 1). 
3. Mice of this race inoculated at from two to ten days old 
show a higher growth percentage than those inoculated at from 
twelve to twenty days old or over. The percentages are 12.87 + 
0.6 and 9.49+0.6, respectively. The difference between the two 
age groups is about four times its probable error. 
4. The difference observed between these age groups is chiefly 
confined to the female sex. The difference between males of the 
upper and lower groups is less than three times its probable 
error. The difference between females of the upper and lower 
groups is seven times its probable error—the percentages in the 
females being 9.39+0.87 and 19.46+1.31, respectively. 
5. Animals of a back-cross generation, some of which should 
possess the factor complex characterizing the susceptible Japa- 
nese waltzing mice and others of which should possess certain 
