GROWTH OF THE FETAL CENTRAL NERVOUS SYSTEM 407 
MATERIAL AND METHODS 
Material 
The material used in this study consisted of 156 human fetuses. 
Fifty-four of these specimens were males, fifty-six were females, 
and the sex of forty-six was unknown. The specimens ranged 
from 3.1 to 53.6 em. in total or crown-heel length and were quite 
evenly distributed between these extremes. At least one speci- 
men was available for each centimeter interval of crown-heel 
length and in many of the centimeter intervals below 30 cm. there 
were three, four, or five specimens. All of the material was 
selected from a much more extensive series of cases, with a view 
to securing specimens in which the brains were well preserved; 
however, a number of brains which were rather soft were used 
for certain measurements which were not affected by this con- 
dition. . 
The great majority of the specimens were fixed in 10 per cent 
formalin to which 1 per cent chromic acid had been added in some 
instances, and all were afterwards preserved in 10 per cent forma- 
lin. Five specimens of the entire series were fixed in Zenker’s or 
Miiller’s fluid and were subsequently preserved in 70 per cent 
alcohol. All of the material had been in the preservation for six 
months or more. 
The effect of formalin fixation upon the fetal brain must be 
known in order to interpret the data correctly. It is unfortunate 
that no comparison has been made between fresh and preserved 
material. The fresh brain of the fetus is too friable for any deli- 
cate, quantitative measurements to be taken upon it. Conse- 
quently, fixation was prerequisite to the collection of the material 
for this study. 
The only checks upon the relationship of fixed and unfixed 
material at our disposal consist of, 1) the determination of the 
effects of formalin upon the size of the fetal body and, 2) the re- 
lation of the curves of fresh brain weight to that of fixed brain 
volume. 
Several investigators have determined the effects of formalin 
fixation on the fetus. Patten and Philpott (’21) record an 
