408 HALBERT L. DUNN 
average increase in the crown-rump length of 4.8 per cent in a 
series of twenty-two pig embryos which had been in 10 per cent 
formalin for six months. Schultze (19) reports an average gain 
in crown-rump length of 2.3 per cent in a group of eighteen human 
fetuses which had been in 10 per cent formalin for nine months. 
The average gain in head length and head breadth of the same 
series was 1.1 per cent and 5.2 per cent, respectively. Calkins 
(21) has found that the effect of fixation on the several diameters 
of the head is very small and that formalin injection causes the 
greatest part of this by a distention of the superficial tissues of 
the scalp. The fetal cranium increases, therefore, very little in 
size when it is fixed by formalin. The brain, on the other hand, 
is supposed to gain greatly in volume. King (10) obtained a 
percentage gain in weight of from 30 to 50 when the brains of 
several white rats were subjected to formalin fixation. Such an 
increase in brain weight or volume could take place in the fetus 
only at the expense of the dural and subdural spaces, since the cir- 
cumference and the diameters of the fetal head are but little 
affected. However, these spaces were found to be quite large in 
most of the preserved specimens in this series. The volume of 
the brain, therefore, could not have been increased to any great 
extent. 
The relationship of the curve of fresh brain weight to that of 
fixed brain volume can be compared readily by tables 2 and 3. 
Table 2 shows the calculated volume of the central nervous system 
for each 5 cm. C H interval. Table 3 sets forth the empirically 
determined values for weights of fresh fetal brains collected from 
the literature. In each respective C H interval the weight is seen 
to be slightly greater than is the volume. This difference may 
be caused in part by the formalin fixation, but the greater part 
seems to be due to the fact that midsagittal sections of the brain 
were made before volumes were determined and that intraven- 
tricular fluid was lost by this procedure. On the whole, there- 
fore, it is doubtful if there is any considerable change of the fetal 
brain volume upon formalin fixation. 
Five cases of the series were subjected to Zenker- or Miiller- 
alcohol fixation instead of formalin. The effects of various 
