560 FUNCTIONS OF THE CEREBRO -SPINAL NERVOUS SYSTEM. 



Oxide of Iron, Fluorine, small quantities of Alkaline Sulphates, and lastly 

 Chloride of Sodium. The quantity of Phosphorus is very large, amounting, 

 according to Borsarelli, 1 to from 1.352 to 1.790 per cent. Perfectly fresh 

 nerves, when at rest, possess a neutral or perhaps slightly alkaline reaction. 2 

 According to Ranke, they become acid after tetanus. The white substance 

 of the brain and spinal cord is also feebly alkaline or neutral. After ex- 

 hausting work and after death it is acid. The gray substance is always 

 acid. :i 



447. As regards the general relations of the principal Centres of the 

 Nervous System of Man, it is only requisite here to remark, that those 

 which make up the Cerebro-Spiual portion of the apparatus have such an 

 intimate structural relation to each other, and so much more frequently act 

 consentaneously than separately, that, notwithstanding the abundant evi- 

 dence of the diversity of their respective endowments, there is considerable 

 difficulty in the determination of their special functions ; since the destruc- 

 tion or removal of any one portion of the Nervous system, not only puts a stop 

 to the phenomena to which that portion is directly subservient, but so de- 

 ranges the general train of nervous activity, that it often becomes impossible 

 to ascertain, by any such method, what is its real share in the entire perform- 

 ance. In this difficulty, however, we may advantageously have recourse to 

 the study of the structure and actions of those forms of the Nervous System 

 presented to us among the lower animals, in which its gangliouic centres are 

 fewer and less intimately connected, and in which, therefore, it is more easy 

 to gain an acquaintance with their several endowments. And from an ex- 

 tensive survey of these, we seem able to deduce the following conclusions, 

 which afford the most valuable guidance in the study of the Nervous System 

 of Man : 4 



I. The Nervous System, in its lowest and simplest form, may consist of but 

 a single gauglionic centre, with afferent and motor nerves, whose function is 

 essentially inter nuncial ; impressions made upon the afferent fibres exciting 

 respondent or " reflex " movements in the muscles supplied by the motor, 

 without any necessary intervention of consciousness. Such movements are 

 properly distinguished as excito-motor. 



ii. A simple repetition of such gauglionic centres may exist to any extent, 

 without heterogeneousness of function, or any essential departure from the 

 mode of action just indicated ; each of these centres may be specially con- 

 nected by afferent or motor fibres with one segment or division of the body, 

 and may minister peculiarly to its actions; but the several centres may be 

 so intimately connected by commissural fibres, that an impression made upon 

 the afferent nerves of any one of them may excite respondent motions in other 

 segments. This we see effected through the annular gangliated cord of the 

 higher Radiata, and through the longitudinal gangliated cord of the Articu- 

 lata ; the disposition of the ganglia and of their connecting cords, having 

 reference simply to the general plan of the body. 



in. A higher form of Nervous System is that in which there is multiplica- 



1 Syd. Sue-. Year-book, 1861, p. 32. 



2 Sec Jleidenhain, Studien des Phys. Instil, zu Brcslnu. 18G8, p. 248; and Lieb- 

 reich, in Tageblatt der INatur-l'orseh Versamm. zu Frankfurt, 1807. 



3 Gscheidlen, Archiv f. L'hysiol., Bd. viii, 1873, p. 172. 



4 Fur a general view of the facts on which these conclusions are based, sec Princ. 

 of Conip. 1'liys., chap, xiii -. 



6 It may, perhaps, bo doubted whether any Animal really exists possosing such a 

 nervous system, and yet not endowed with consciousness. It is quite certain, how- 

 over, that, animals do exist (the Tunicated Mollnsea for example) in which the actions 

 above referred to are tho only ones of which we have any distinct evidence from ob- 

 servation of their habits. 



