GROWTH OF THE FETAL CENTRAL NERVOUS SYSTEM 409 
fixing fluids upon brain tissues have been determined by King 
(10) and Hrdliéka (06). The work of King was done upon the 
brain of the rat, and is analogous, in all probability, to the effects 
of the fixing fluids upon the fetal brain. Calculated from her 
findings, the absolute values of the five fetal brains subject to 
Zenker- or Miiller-aleohol fixation would be 10 to 40 per cent 
lower than the brains which were fixed by formalin. ‘Three of the 
fetal brains in the present series which were fixed by the Zenker- 
or Miiller-aleohol method lie in the C H interval of 5 to 10 em. 
and two are in the C H interval of 10 to 15 cm. A glance at 
figure 2 shows that these cases adhere closely to the central 
tendency. Hrdlicka subjected the brains of twenty-seven mam- 
mals and birds to 10 per cent formalin fixation. ‘Ten sheep brains 
showed an average increase of 13 per cent after one month of 
fixation; seven brains of birds an average gain of 20 per cent and 
six brains of various mammals about 24 per cent. He left the 
brains in 10 per cent formalin for eighteen months, and then 
found that they had decreased in size to about 92 per cent of 
their original weight. 
From the results of these investigators as well as the data of 
this series, it is obvious that 10 per cent formalin fixation has a 
comparatively slight effect upon the volumetric determination of 
the fetal brain. 
Methods of collecting data 
The magnitudes and proportions of the various parts of the 
central nervous system were determined by several different 
methods—by lineal measurements, by weighing and determining 
the volume of each part, by making tracings of median sagittal 
sections, and by photographing the lateral surfaces of the speci- 
mens. The details of these methods and the descriptions of the 
measurements taken will be considered separately. 
Lineal measurements. All lineal measurements were made with 
a steel vernier caliper which could be read accurately to 1 mm. 
by the major and to 0.1 mm. by the minor scale. ‘They were 
made with the brain and spinal cord in situ and always represented 
the shortest distance between two given points. 
