The form in which nervous matter first de velopes itself as a distinct tissue is in that of threads or cords, into the composition of which areolar tissue and bloodvessels generally enter. The class of animals in which this arrangement prevails has been designated by Mr. Owen 1Vematoneura; and, in many of these at least, the existence and the disposition of grey matter have yet to be ascertained.
The nervous matter of both kinds is a sub stance of extreme softness and delicacy, liable to break up under the least pressure ; the nervous tissue owes much of its physical tena city to the other tissues which are associated with it, and to the numerous bloodvessels which play among its elements.
The chemical composition of this matter has been an object of investigation with several observers, but it is remarkable that few com parative analyses of the two kinds of ner vous matter have been made with a view to determine on what the differences between them depend ; and, indeed, such an analytical investigation is as yet a great desideratum. The part which has chiefly been selected for analysis is the brain, in which doubtless both kinds of nervous matter were indiscriminately examined.
Among the earliest investigations of this kind were those of Leming; some time afterwards Thouret examined the brain ; and still later Foureroy. The last writer notices the large admixture of water with the cerebral substance, and points it out as one of those animal sub stances in which water exists in the largest pro portion ; from constituting, as- it does, three fourths or four-fifths, and in many instances seven-eighths of its vveight. Vauquelin's ana lysis, made in 1812, gave a considerable insight into the true composition of the brain. This chemist showed that the cerebral substance is an emulsive mixture of albumen, fatty matter, and of water, the last holding in solution certain saline and other ingredients common to the brain with other parts of the body. By solu tion in boiling alcohol, Vauquelin was enabled to obtain the two constituents of the fatty substance, namely, the elaine and stearine (marg,arine). Vauquelin also recognised the presence of phosphorus in the brain. His ana lysis yielded the following result:— John, who specially analysed the grey ner vous matter, states that it is deficient in fatty matter, and that its albumen is less tenacious than that of the white. And Lassaigne states
that the grey substance is deficient in white fatty matter, but contains a greater proportion of red, 3.7 per cent. being the amount con tained in the grey, and 0.9 per cent. in the white.* Vauquelin remarks that the medulla oblon gata and the medulla spinalis have the same composition as the brain, but contain a. much greater quantity of cerebral fat, with less albu men, osmazome, and water.
M. Couerbe's elaborate analysis does not ap pear to be entitled to much confidence, since the compounds into which he resolved tte cerebral matter did not, on analysis, alwaY., present the same composition. This variation of ele mentary constItution he attributed to physiolo gical differences in individuals.
The latest and apparently the most complete analysis of the brain is that by Fremy, pub lished in the Annales de Chimie for 1841. In the main his results agree with those of Vauquelin.
Ile states that the cerebral mass is formed, as had been already shown by Vauquelin, of an albuminous matter containing a great quan tity of water, and which is found mixed with a peculiar fatty matter ; and that these different substances exist in the following proportions, seven parts of albumen, five parts of fatty matter, and eighty parts of water.
The chemical examination of the albuminous matter yields nothing of importance. This sub stance is insoluble in water, in alcohol, and in ether. M. Fremy's principal care has been to determine the composition of the Fatty matter, and this he has endeavoured to do by an ana lysis of the brain in different animals, but prin cipally in man.
His method of proceeding is, to cut the brain into small pieces, and to treat it with successive portions of boiling alcohol,leaving them for some days in contact with the spirit. The object of this is to remove from it its large quantity of water, which interferes with the action of ether upon it. The coagulated mass thus obtained is submitted to pressure, is divided rapidly in a mortar, and is then treated by ether, first cold and subsequently hot; the resulting fluids when submitted to distillation yield a viscid residue, which is called the ethereal product.