722<3 



PHYSIOLOGY OF THE NERVOUS SYSTEM. 



but to the vigour and health of the body also ; 

 that to ensure the full developement of the 

 wens saua we must secure the possession of the 

 corpus sanum. 



Certain diseases are evidently associated 

 with disturbed or excited states of emotion. 

 In such cases, the nerves most affected are 

 those connected with the mesocephale and 

 medulla oblongata, denoting an excited state of 

 these portions of the encephalon. Of these 

 diseases the most remarkable are hysteria and 

 chorea; both of which may be induced either 

 by a cause acting primarily upon the mind, or 

 by functional disturbance of the body, as de- 

 ranged assimilation, in persons of a certain 

 character of constitution. In hysteria, the 

 globus, the tendency to cry or laugh, the dis- 

 turbed breathing, the variously deranged state 

 of the respiratory acts, all denote affection of 

 most, if not all, the nerves coming from these 

 segments. In chorea the frequent movements 

 of the face and eyes, the peculiar and very 

 characteristic mode of protruding the tongue, 

 the impaired power of articulation, are depen- 

 dent on an altered state of that part in which 

 the portio dura of the seventh pair, the third, 

 fourth, and sixth, and the ninth nerves are 

 implanted. In both diseases the principal 

 central disturbance is in the mesocephale; and 

 this may be caused either by the direct in- 

 fluence of the mind upon it, or by the propa- 

 gation of a state of irritation to it from some 

 part of the periphery. Chorea, even of the 

 most violent and general kind, is very commonly 

 produced by sudden fright; and it is well 

 known how frequently mental anxiety or ex- 

 citement developes the paroxysm of hysteria. 



There is no part of the cerebro-spinal centre 

 which appears to exercise such extensive sway 

 over the movements and sensations of the body 

 as this portion, the mesocephale, which may be 

 regarded as the centre of emotional actions. 

 Its influence extends upwards to the cerebral 

 convolutions backwards to the cerebellum 

 downwards to all the nerves of sensation and 

 motion. Through its connection with the pos- 

 terior horns of the spinal grey matter, it can 

 excite the sensitive as well as the motor nerves 

 of the trunk. Hence it is not to be wondered 

 at that a highly disturbed state of this centre is 

 capable of deranging all the sensitive as well as 

 motor phenomena of the body and even the 

 intellect. Hence we may explain the extra- 

 ordinary movements in hydrophobia and ge- 

 neral chorea, in both of which diseases this 

 part of the nervous centre is doubtless affected. 

 It has often been remarked how much more 

 powerful are the voluntary actions when 

 prompted by some strong emotion, than when 

 excited only by an effort of the will, liage, 

 or despair, is able to magnify the power of the 

 muscles to an incalculable degree. This may 

 be due to the increased stimulus derived from 

 the influence of the centre of emotion being 

 conjoined with that of the centre of volition. 



The intimate connection of the olivary co- 

 lumns with the grey matter of the cord, and 

 through that with all the roots of the spinal 

 nerves, illustrates the power of emotional 



changes upon the organic processes. How 

 often does the state of the feelings influence 

 the quantity and quality of the secretions, no 

 doubt through the power of the nerves over 

 the capillary circulation ! Blushing is pro- 

 duced through an affection of the mind, acting 

 primarily on the centre of emotion, and 

 through it on the nerves, which are distributed 

 to the capillary vessels of the skin of the face. 



The sexual passion must be ranked among 

 the mental emotions. Like them, it may be 

 excited and ministered to by a certain line of 

 thought, or by particular physical states of the 

 sexual organs. It seems, therefore, more cor- 

 rect to refer this emotion to the common centre 

 of all, than to a special organ according to 

 Gall's theory; and it may be remarked, that 

 great developement of this part of the brain is 

 just as likely to produce great width of cranium 

 in the occipital region as a large cerebellum. 



Of tlte Junctions of the cerebellum. All ana- 

 tomists are agreed in admitting, in the whole 

 vertebrate series, (the amphioxus, perhaps, ex- 

 cepted,*) the existence of a portion of the en- 

 cephalon which is analogous to the cerebellum. 

 This extensive existence of such an organ indi- 

 cates its great physiological importance, as a 

 special element of the encephalon. The ce- 

 rebellum exhibits much difference both as re- 

 gards size and complexity of structure in the 

 different classes ; and although, upon the 

 whole, it increases in its developement in the 

 same ratio as the hemispheric lobes, it exhibits 

 no constant relation of size to those parts. 



The large size and complicated structure of 

 this organ in the higher vertebrate animals, 

 and its distinctness from the cerebrum, for its 

 commissural connection with that segment of 

 the encephalon is not extensive, have excited 

 the interest and curiosity of speculative physio- 

 logists ; and, accordingly, we find no part 

 respecting which a greater variety of hypotheses 

 have been suggested, most of them being en- 

 tirely devoid of foundation. The experiments 

 of Flourens have, however, thrown more light 

 on this subject than any previous observations ; 

 and his hypothesis appears nearer the truth than 

 any which has been proposed. 



The facility with which the cerebellum may 

 be removed or injured, especially in birds, 

 without involving the other segments of the 

 brain, renders it a much more favourable ob- 

 ject for direct experiment than them. A skil- 

 ful operator may remove the greater part or the 

 whole of the cerebellum without inflicting any 

 injury on the hemispheres or other parts. 



Flourens removed the cerebellum from pi- 

 geons by successive slices. During the removal 

 of the superficial layers there appeared only a 

 slight feebleness and want of harmony in the 

 movements, without any expression of pain. 

 On reaching the middle layers an almost uni- 

 versal agitation was manifested, without any 

 sign of convulsion : the animal performed rapid 

 and ill-regulated movements; it could hear and 



* The observations of Quatrefages render it 

 doubtful that even the amphioxus can be regarded 

 as forming an exception. Ann. des Sc. Nat., 1846. 



