GROWTH OF THE CEREBRAL CORTEX 181 
(b, e, and g) for control. The experiment was begun five days 
after birth. One test rat (f) and one control (g) were killed by 
the mother. For the first three days mild starvation was tried, 
and then, from the age of nine days, severe starvation was 
instituted. They were killed for examination at the ages of 15, 
17, and 28 days. 
Litter D (born October 23, 1916) consisted initially of eight 
young, of which five (a, c, d, e, and g) were used for experiment 
and three (b, f, and h) for control. One underfed (g) and one 
control (h) were killed by the mother. In this litter severe 
starvation was begun at the age of three days. The animals 
were killed at the ages of 9, 10, 16, and 18 days. 
Litter E (born November 4, 1916) was composed of eight rats, 
of which six (a, b, e, d, g, and h) were selected for experiment and 
two (e and f) for control. Severe starvation with some intervals 
of feeding was begun at the age of three days. In this litter pairs 
of test rats of the same age were killed for examination (on the 
7th, 10th, and 17th days of the experiment) to determine indi- 
vidual variations. 
Litters D and E represent groups in which relatively severe 
starvation was begun at an early age. 
Series II (Litters F and H) 
Procedure. In this series one nursing mother was placed in 
charge of an excessive number of young. The results were not 
very good, because some relatively lucky or strong ones always 
got more than their share of milk, while the others were in a con- 
dition of severe underfeeding. 
Litter F (born October 15, 1916). To a young small primipara, 
which had just given birth to ten young, were entrusted ten more 
young from two other litters which had been born on the same 
day. Unhappily, the young from three different litters were 
not separately marked. The rate of growth among them was 
later found to be unequal, owing probably partly to litter char- 
acteristics and partly to the inequality of the milk ration. Indi- 
viduals were selected arbitrarily and killed for examjnation at 
intervals of one to three days (at the ages of 11, 14, 17, 19, 
