Ranson, Fibers in Leszons of the Brain. 195 
ments were sterilized in boiling water; the site of the wound 
was freed from hair and washed in mercuric chloride, I-1000. 
After the operation the opening was sealed with collodion. 
It was not until many failures had been made that success 
was attained in raising the rats operated on during the first 
week of life. In the first cases when they were returned to the 
nest the mother ate them, and when fed by hand they could be 
kept alive for only a short time. Others working in this labo- 
ratory have experienced the same difficulty. It was supposed 
that the action of the mother was caused by some foreign odor 
clinging to the young rat after it had been handled. A certain 
degree of success, however, was secured by keeping the young 
in an incubator heated nearly to the body temperature, and 
forcing the mother, kept in a cage near by, to nurse them at 
regular intervals (every four hours during the day and eight 
hours at night). By this means some young were kept alive 
for ten days. It was found that as long as the young were 
kept warm the mother could safely be left with them and that 
after a time she would care for them of her own accord. It 
was also found that if the animals were taken from the nest 
under conditions which prevented the loss of body-heat, they 
could be returned to the mother with safety. For this purpose 
a jar was warmed to body temperature and filled with hot cot- 
ton. In this the rat was carried from the nest to the opera- 
ting room, where it was placed in an incubator until all was 
ready. The rat was held ina hot cloth during the operation, 
which was performed in a few minutes and without anaesthet- 
ics. It was then returned to the hot jar and carried back to 
the animal room. When these precautions were observed the 
mother never refused to care for the young. 
After the operation the rats were allowed to live for one 
month anda half. The brains were then removed, hardened 
in MULLER’s fluid at 40° C. for one month and imbedded in cel- 
loidin. The occipital region of each brain was cut in serial 
frontal sections 45 yw thick and stained by the PaLt-WEIGERT 
technique. Also for comparison the brain of a rat, operated 
on at the age of four days and killed thirty-two days later, was 
