FUNCTIONS OF THE CEREBRO-SPIN AL NERVOUS SYSTEM. 559 



which the continuity of the perineurium is restored. According to some, 

 bipolar cells are developed within this sheath, the processes of which unite 

 to form the axis-cylinders of new nerves; the medullary sheath being sub- 

 sequently developed around them. But Rauvier maintains that the fibres of 

 the periphcric stump atrophy, and that the new fibres proceed from the axis- 

 cylinder of the centric stump which make their way through the cicatrix 

 into the degenerated fibres, or run in the connective tissue of the peripheric 

 stump. The changes that occur in the fibres after section are, that they be- 

 come cloudy, and their margins are less defined. These changes are well 

 marked on the eighth day, and soon after the medullary substance becomes 

 divided into segments, and a kind of coagulation takes place in it, with de- 

 posit of fat-globules. In the course of a month or six weeks the medullary 

 substance is reduced to a mass of extremely fine granular molecules of fat- 

 like dust, which finally disappear, and the sheaths collapse. Whether the 

 cylinder-axes remain for a long time unaltered, as SchifT 1 maintains, or also 

 undergo absorption, as Rauvier believes, is still doubtful. The time that 

 elapses before the newly-formed tissue can fulfil the function of a nerve in 

 transmitting sensory and motor impulses is given by various authors at from 

 7-15 days for the first traces, and 30-90 days for complete return of sen- 

 sation and motion. 2 According to Schiff, 3 regeneration of the pueurnogastrics 

 may occur even when two inches have been excised. It is questionable 

 whether, after extirpation of a ganglion, new ganglionic corpuscles can be 

 formed ; yet, in Brown- Sequard's experiments upon pigeons, it was found 

 that the whole spinal cord would reunite after division, with almost complete 

 restoration of function. The distal extremity of a nerve separated from its 

 centre by section undergoes fatty degeneration, 4 whilst the proximal portion 

 retains for a considerable period its normal characters, indicating, according 

 to Waller, that the ganglion-cell with which it is in relation exercises a cer- 

 tain influence over its nutrition. 



446. As regards the chemistry of the Nerves, it has been found that the 

 Brain contains about 75 per cent, of water, and 25 of solid residue, of which 

 about 15 parts consist of fatty substances, 7.5 of albuminous compounds, 1.5 

 of salts, and 1 of extractive matters. The proportions of these constituents, 

 however, are different in other parts of the nervous system ; the amount of 

 water, for instance, varying from 70 (in the white) to 85 per cent, (in the 

 gray substance). The fat contained in the gray matter is always much 

 smaller in quantity than that in the white. According to Peilo\vsky, D when 

 dried the gray substance contains more than half of its weight of albumen, 

 the white only one quarter. The gray substance (dried) contains 18.7 of 

 Cholesterin and fat, and 0.5 of Cerebrin, the white 51.9 of the former, 

 and 9.5 per cent, of Cerebrin. Amongst the chief constituents of the cere- 

 bral substance, in addition to Cerebrin, is Lecithin, with the products of its 

 decomposition, viz., glycerin, phosphoric and oleo-phosphoric acids, and 

 other fatlike substances containing phosphorus and soluble in ether, palmitic 

 acid, small quantities of ordinary fat, and volatile fatty acids. Besides 

 these, the following substances are enumerated by v. Gorup-Besanez, 6 

 an albuminous substance resembling Myosin, a substance analogous to 

 Elastin, small quantities of a soluble albuminous substance, coagulating at 

 147 F. ; Inosite, Sarkin, Xauthin, Kreatin, Lactic, Uric, and Phosphoric 

 acids, and their combinations with Potash, Lime, and Magnesia ; Silicic Acid, 



1 Comptes Eendus de I'Academie des Sciences, Mars 6th, 1854. 



5 Dt-scot, These Inaugurate, 1822; Paget, Surgical Pathology. 



3 Vierordt, Physiologic, 1861, p. 44. 4 See Sohitt', Physiologic, p. iii. 



6 Pfluger's Archiv, 1873, p. 369. 6 Phy.-. Chemie, 1875, p. 697. 



