CHEMICAL COMPOSITION OF NERVOUS MATTER. 223 



the continuity of whose nerve-fibres cannot be distinguished near their 

 apices. Here, however, the history of the development of the nervous 

 plexuses in the skin seems to show, that the fibres may be considered as 

 commencing in a peripheral ganglionic expansion ; for it has been shown 

 by the observations of Prof. Kolliker upon the tail of the tadpole, that 

 the nervous plexuses are formed in the same manner as the capillary 

 netwrok ; namely, by the inosculation of the prolongations of radiating 

 cells, whose centres are at a considerable distance from each other. 

 Hence it is probable that cell-nuclei, or some equivalent centres of force, 

 remain in connexion with the peripheral nerve-fibres of the skin and 

 tongue, as with those of other sensory surfaces. Sometimes the ultimate 

 plexuses seem to be formed in the Skin, as in Muscle, by the subdivision 

 of the primitive fibres ( 341). 



383. We have now to speak briefly of the Chemical Composition of 

 the Nervous matter ; a consideration which will be presently shown to 

 be of much importance. As formerly remarked ( 7), the vital activity 

 of a tissue is usually greater, as the proportion of its solid to its fluid 

 contents is less ; and this rule holds good most strikingly in regard to 

 the Nervous substance, the vital activity of which is far greater than 

 that of any other tissue, and the solid matter of which usually consti- 

 tutes no more than a fourth, and occasionally does not exceed an eighth 

 of its entire weight. The proportion of water is greatest in infancy and 

 least in middle life ; and it has been observed to be under the average 

 in idiots. Of the solid matter of the brain, about a third consists of 

 fibrine or albumen ; which is probably the material of the membrane of 

 the tubuli, as well as of the tissue that connects them. It is chiefly with 

 the Fatty matter, which constitutes about a third of the solid substance, 

 that the attention of Chemists has been occupied. This is stated by M. 

 Fremy (one of the most recent analysts) to contain, besides the ordinary 

 fatty matters, and Cholesterine or biliary fat, two peculiar fatty acids, 

 termed the Cerebric and the Oleo-phosphoric. Cerebric acid, when puri- 

 fied, is white, and presents itself in crystalline grains. It contains a 

 small proportion of Phosphorus ; and differs from the ordinary fatty 

 matters in containing Nitrogen, as also in containing twice their propor- 

 tion of oxygen. Oleo-phosphoric acid is separated from the former by 

 its 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 re- 

 solves itself into a pure oil, which is elaine, while phosphoric^ acid re- 

 mains in the liquor. The proportion of phosphorus in the brain is con- 

 siderable ; being from 8 to 18 parts in 1000 of the whole mass, or from 

 l-20th to l-30th of the whole solid matter. It seems to be unusually 

 deficient in the brain of idiots. The remaining third and sometimes 

 more, is composed of a substance termed Osmazome (which seems to be 

 a proteine-compound in a state of decomposition), together with saline 

 matter. No satisfactory examination has yet been made into the com- 

 parative composition of the vesicular and fibrous substances ; but accord- 

 ing to Lassaigne, the former contains much more water than the latter, 

 and little colourless fat, but nearly 4 per cent, of red fat, which does 

 not exist in the other. 



384. Various circumstances lead to the belief, that the Nervous tissue, 



