THE NERVOUS SYSTEM. . 95 



from flattening it against the side of the jar while soft, 

 and immerse it in the following liquid to harden. 



Potassium bichromate 10 grams. 



Formalin or formaldehyde 40 per cent . . . 15-20 c.c. 

 Water 500 c.c. 



Allow it to remain in this liquid two weeks, and then 

 remove and wash it in running water for two or three 

 hours. If it is not sufficiently hard, let it stand over- 

 night in a mixture of 350 c.c. of 5 per cent formalin and 

 150 c.c. of 95 per cent alcohol. If a fresh brain be placed 

 in this latter mixture, it will harden throughout, with no 

 appreciable shrinkage, to the consistency of India rubber 

 within thirty-six hours, but there will be no differentiation 

 of white and gray matter. 



The potassium bichromate colors the cellular (gray) 

 tissue, but has no effect upon the fibrous (white) tissue, 

 while alcohol bleaches both tissues. 



I. THE BRAIN AS A WHOLE. 



a. What is its position, size, and shape ? 



b. The surfaces of the brain. 



1. The dorsal surface is the upper or more rounded 



surface. 



2. The ventral surface is the lower or flatter surface. 



3. The anterior end is more rounded than the 



posterior. 



II. THE COVERINGS OF THE BRAIN. 



a. The dura mater is the thick outer covering. 



1. Is it attached to the brain ? 



2. Is it close to the brain? 



