184 NAOKI SUGITA 
20, 23, 24, 26, 30, and 40 days). Those killed were replaced 
by individuals of like age from other litters, so as to keep the 
number in this litter always above thirteen. After twenty days, 
the mother was removed and the young fed with a small amount 
of ordinary food. ‘The last eight young, which survived beyond 
the age of forty days, were rejected as too old for the purpose of 
this study. 
Litter H (born January 2, 1917). A mother having just given 
birth to eight young was entrusted with nine more young from 
another litter which had been born on the same day. The 
underfed young of this litter were all employed for the study on 
the percentage of water and for the histological study of myelina- 
tion in the brain and not included in the study of the cerebral 
cortex. 
Series IIT (Litter G) 
Litter G (born October 23, 1916). In this series a nursing mother 
was severely underfed immediately after the parturition. This 
litter consisted of eleven young. Only a fraction (one-tenth to 
one-twentieth) of the ordinary diet with unlimited water was 
supplied daily to the mother. She was found to lose slowly 
in body weight day by day. The amount of milk was conse- 
quently much reduced, but not completely stopped, as could be 
determined by examining daily the stomach contents of the 
young. By this method I was able to get a series of young which 
were very poorly developed. The young were killed for exam- 
ination at the ages of 8, 10, 11, 12, 15, 16, 18, 22, and 25 days. 
Table 2 contains the observed body weight and brain weight of 
the young in Litters F, G, and H, when examined, for a com- 
parison with table 1. 
4. BODY WEIGHT, BODY LENGTH AND TAIL LENGTH 
Table 3a (not published, because of its complexity, but on file 
at The Wistar Institute).-gives for each individual in this study 
the sex, age, observed body length, tail length, and brain weight. 
The standard tail length and the standard brain weight for the 
observed body length were also entered for comparison, the 
