GROWTH OF THE CEREBRAL CORTEX AL 
no matter what the age of the brain is. It takes only a couple 
of hours to complete fixation in this fluid, if the fluid is kept in 
the oven at 37°C., but, as a matter of convenience, I left each 
brain in 20 ee. of this fluid for 24 hours at the room temperature. 
By this treatment the form of the cells was well preserved, even 
after imbedding in paraffine (1A) (figs. 3 and 4). 
Comparing this with the material which was fixed in the same 
fluid but imbedded in ecelloidin (1B), the contours of cell bodies 
were, in the former, somewhat indistinct and the size of the 
nuclei somewhat larger (fig. 1, ¢). But after paraffine imbedding 
the nuclei have yet good contours which are not zigzag and the 
Fig. 1 Showing pyramids from the lamina pyramidalis at a fixed locality 
(locality VII) of the cerebral cortex of Albino brains weighing 1.3 to 1.5 grams. 
Magnification of about 950 diameters, measured directly on the slide. a = from 
a brain imbedded in paraffine after fixation in 95 per cent alcohol. b = from a 
brain imbedded in paraffine after fixation in 4 per cent formaldehyde. c = from 
a brain imbedded in celloidin after fixation in Bouin’s fluid. 
so-called Nissl bodies are also well stained. Since paraffine was 
used exclusively for the imbedding medium, Bouin’s fluid proved 
to be the best fixative for the albino rat brain, when it is re- 
quired to follow the growth changes of the cortex by the measure- 
ments of the cells of the cortex. 
Figure 1 shows a comparison of the effects of several fixatives 
on the shape and contours of the cell bodies and the nuclei when 
applied to albino rat brains of like age. The examples are all 
from Albino brains weighing 1.3 to 1.5 grams and represent 
pyramids in the lamina pyramidalis taken near the locality VII 
in frontal sections, being comparable with VII in figure 2, a 
and b. 
