Effects of External Conditions 117 
2% months old at the time. Many of them did not become preg- 
nant till they were much older than this, however, while it is well 
known that female mice may bear healthy young at an even earlier 
age. Again, when judged by most other standards, the animals 
appeared to be in perfect health. ‘They were active enough, and 
the fur was commonly in good condition, though the size of the 
females, at least, even when fully grown, was probably somewhat 
below normal. Moreover, after the earlier weeks of life, their 
mortality had been slight. That this damage to the generative 
powers must be set down as one of the results of the experimental 
conditions seems, nevertheless, probable. 
Measurements at 42 Days. ‘The weight and tail length of these 
mice was taken at the age of six weeks." No other measurements 
were at that time believed to be practicable with the living 
animals. The following table (no. 3) presents the mean and the 
index of variability for each of these measurements, the two sexes 
being treated separately. 
TABLE 3 
Series of 1907-1908: Measurements at six weeks of age 
WEIGHT ‘ | TAIL LENGTH 
Males Females Males | Females 
| Warm Cold Warm | Cold | Warm | Cold | Warm | Cold 
(29) (31) (33) (23) Rag) (Gays sic! Ga) 
| 
Mean...............| 12:997 | 13.123 | 12.282 | 11.400] 68.83 | 54.16 | 69.06 
51.91 
| 40.270 | +0.374 | 40.179 | 40.301 | $0.35 |0.68 | +0.43:| +0.83 
Standard deviation....| 2.156 | 3.088 M7 2.138 2.80 5 09" lgneg 5.89 
| 0.191 | 0.265 | 0.126 | 0.212 | £0.25 | +0.48 | 0.31 | £0.59 
Fig. 2 shows the distribution of weights for the cold and warm 
room groups (sexes combined); Fig. 3 shows the distribution of 
tail lengths for the two groups. From the table and polygons 
collectively the following facts may be gathered: 
*1 Owing to difference in the date of birth, this age was not attained simultaneously. The great 
majority, however, were born within the space of a week. 
