214 



ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 



solubility in ether : it is of a viscid consistence ; but when boiled for a long time in water or 

 alcohol, it gradually loses its viscidity, and resolves itself into a fluid oil, which is pure 

 Oleine, whilst phosphoric acid remains in the liquor. The proportion of Phosphorus which 

 this oil contains is about 2 per cent. Cholesterine has also been extracted from the brain by 

 M. Fremy in considerable quantity. The proportion of Fixed Salts is small; not being 

 above 3^ parts in 100 of Dry Cerebral matter ; which is less than half the proportion that 

 exists in Muscle. According to Lassaigne, the chemical composition of the Cortical and 

 Medullary substances of the brain is essentially different; the former containing 85 per 

 cent, of water, whilst the latter has only 73 ; the cortical substance having also 3'7 per cent. 

 of a red fatty matter, of which the medullary has scarcely any; and being almost entirely 

 destitute of the white fatty matter, which exists in large proportion in the latter. 



The Albuminous matter in the above analyses, is probably that of which 

 the walls of the nerve-cells and nerve-tubes, and of the capillary blood-vessels 

 are composed. The contents of these cells and tubes are represented chiefly, 

 if not entirely, by the phosphorized fats ; and there are many reasons for re- 

 garding these as the active agents in the operations of the Nervous system. 

 It will be remarked, that the amount of phosphorus is the greatest at the 

 period of greatest mental vigour ; and that in infancy, old age, and idiocy, the 

 proportion is not above half that which is present during the adolescent and 

 adult periods. 



250. The Nervous System is very copiously supplied with blood-vessels ; 

 the arrangement of which varies according to the form of the elementary parts, 

 in which they are distributed. Thus in the Vesicular substance of the ner- 

 vous centres, the capillaries form a minute net-work, in the interstices of which 

 the ganglionic cells are included. In the tubulo-fibrous substance, the capilla- 

 ries are distributed much on the same plan as in Muscular tissue ; the net- 

 work being composed of straight vessels, which run along the course of 

 the fibres, passing between the nerve-tubes, and which are connected at 

 intervals by transverse branches. And at the sensory extremities of the 



Fig. 121. 



Fig. 122. 



Capillary net-work of Nervous Centres. 



Distribution of Capillaries at the sur- 

 face of the skin of the finger. 



nerves we find loops of Capillaries arching over their terminal and probably 

 looped filaments. The Brain of Man, taken en masse, has been estimated to 

 receive one-sixth of the whole amount of blood, although its weight is not 

 usually more than a-fortieth part of that of the entire body. Whether or not 

 this estimate be precisely correct, there can be no doubt that it receives far 

 more blood, than any other part containing the same amount of solid matter. 

 Now this copious supply of blood evidently has reference to two distinct ob- 

 jects ; first, to supply the necessary conditions for the action of the Nervous 

 system ; and, secondly, to maintain its nutrition. Many circumstances lead 

 to the conclusion that, in the Nervous as in the Muscular system, every vital 

 operation is necessarily connected with a certain change of composition, so 



other chemists give a much higher proportion to the phosphori/ed f;it, and a much smaller 

 one to the ill-delined compounds represented l>y the designation Osmazome. 



