774 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



adjacent cells, so that impulses may be conducted from one to the other. 

 In the peripheral ganglia connective-tissue corpuscles surround the 

 nerve-cells. 



I. CHEMICAL AND PHYSICAL CHAKACTEEISTICS OF NERVOUS 



TISSUES. 



The composition of nervous tissue varies according as the examina- 

 tion is made of the white matter of the cerebrum or of the spinal cord, 

 or of the gray matter. The following table represents their average 

 composition : — 



Chemical Composition of Nervous Tissue. 



Gray Matter. White Matter. 



Water 81.6 68.4 



Solids, 18.4 31.6 



Proteids 55.4 24.7 



Lecithin, 17.2 9.9 



Oholesterin and fats, .... 18.7 52.1 



Cerebrin 0.5 9.5 



Substances insoluble in ether, . .6.7 3.3 



Salts 1.5 0.5 



When brain-matter is incinerated the greater part of the phosphorus 

 of the lecithin becomes phosphoric acid, and the ash, hence, has an acid 

 reaction. The following is the composition of the ash of one hundred 

 grammes brain after removing lecithin: — 



S0 4 K 2 0.411 



KC1 2.524 



K 2 HP0 4 , 0.266 



Ca 3 P 2 8 0.013 



MgHP0 4 0.084 



Na 2 HP0 4 . 1.752 



Na 2 C0 3 1.148 



Excess C0 2 , 0.082 



FeP 2 0, 0.010 



6.290 



The reaction of the gray matter during life is said to be acid from 

 the presence in the ganglionic masses of lactic acid. The reaction of 

 the white matter is neutral or alkaline. 



From the above table it is seen that more than half the solids in the 

 gray matter and about one-fourth the solids in the white matter of the 

 nerve-centres consist of proteids, and yet our knowledge of these bodies 

 is very imperfect. 



The proteids consist of albumen, which is found in the axis cylinder 

 and in nerve-cells; it is soluble in water and coagulates at 75° C; a 

 globulin-like substance, which may be extracted by means of a 10 per 

 cent, solution of common salt, and which is precipitated by dilution with 

 water and by saturation with salt ; and alkali albuminate, which remains 



