CONNECTION OF FIBROUS AND VESICULAR SUBSTANCES. 



213 



Terminal nerves on the sac of the second 

 molar tooth of the lower jaw in the sheep, 

 showing the arrangement in loops. (After 

 Valentin.)] 



ing the dental saceuli, in the expansions of [Fig. 120. 



the auditory nerve distributed upon the de- 

 licate membrane lining the cavities of the 

 internal ear, and elsewhere. It would yet, 

 however, be premature to say, that this ar- 

 rangement is universal. The peripheral 

 extremities may be really considered as 

 the origins of the sensory nerves ; since 

 it is in them that those changes are ef- 

 fected which it is the office of the trunks 

 to conduct towards the centres ; and it may 

 be reasonably inquired, whether anything 

 like the vesicular substance of the ganglia 

 can be detected in them. In examining 

 the retina microscopically, it is found to 

 be almost entirely made up of a layer of 

 ganglionic cells, very closely resembling 

 those of the grey matter of the brain; and 

 these are in apposition with the vascular 

 layer; so that we have here precisely the 

 same provision for exciting a change, that 

 is to be conducted towards the centres, as 

 we have in the brain for exciting a change, 

 whose influence is to be conveyed towards 

 the periphery. Something of the same 

 kind has been seen in connection with the 

 corresponding expansions of the olfactive 

 and auditory nerves ; and it is probable 

 that similar elements exist in the papillae 



of the skin and tongue, to which the nerves of taste and touch are distributed. 

 In these papillae we find loops of capillary vessels in close contiguity with 

 the extremities of the nerve-tubes. Hence we may state it as a general fact, 

 that wherever a change is to be originated, we find some form of Vesicular 

 matter, with capillary blood-vessels ; whilst for the conduction of such a 

 change to distant parts, the Fibrous structure is alone required. 



249. The Chemical constitution of the Nervous matter is peculiar ; and 

 an acquaintance with its general features is of importance, in leading us to 

 recognize in the excretions the results of its decomposition. 



a. The following, according to L'Heritier, is the relative proportion of the different con- 

 stituents in individuals of different classes : 



Aged 



Infants. Youths. Adults. '. 

 Water 

 Albumen 

 Fat . 



Osmazome (?) and Salts 

 Phosphorus 



It appears from the researches of M. Fremy, that the Phosphorus is combined with part of 

 the fatty matter; and forms with it two peculiar fatty acids, termed by him the Cerebric and 

 Oleophosphoric. Cerebric acid, when purified, is white, and presents itself in crystalline 

 grains. It contains a small proportion of Phosphorus ; and differs from the ordinary fatty 

 matter, in being partly composed of Nitrogen. It consists of 66-7 per cent, of Carbon, 10-6 

 of Hydrogen, 2-3 of Nitrogen, 19-5 of Oxygen, and O9 of Phosphorus; and thus differs from 

 ordinary fat, not only in containing Phosphorus and Nitrogen, but in possessing more than 

 twice their proportion of Oxygen.* Oleophosphoric acid is separated from the former by its 



* It is probable that, in the above analysis of L'Heritier, the Cerebric acid, which is not 

 soluble in ether, is included under the head of Osmazome ; for the analyses of Denis and 



