XXXI V] THE CEREBKUM AND CEREBELLUM 275 



NOTES. 



The fresh brain is taken without the dura mater or with it 

 freely opened, and placed in 2 p.c. ammonium or potassium bichro- 

 mate ; on the following day it is cut into pieces and placed in fresh 

 potassium bichromate for 1 to 3 months ; then treated in the 

 manner given for the spinal cord, p. 242. 



Instead of a rabbit's brain the brain of a cat or dog may be 

 taken ; a solution of the chromium salt may advantageously be 

 injected into the basilar artery, but even then it is not easy to 

 preserve the natural form of the cells of the 3rd and 4th layers of 

 the cortex ; the structure of the cortex in the cat and dog differs 

 also at different points more than in the rabbit, the chief points 

 of difference being the occurrence of very large cells in groups or 

 singly in the lower part of the third layer, and the variation in 

 number and extent of the angular cells, which may spread into 

 the third layer or may be inconspicuous. 



In staining with picrocarmine, it is perhaps best to cut 

 sections by the freezing method as soon as the tissue is hardened 

 in potassium bichromate, and before placing in alcohol. 



For other methods cp. p. 243. 



182 



