332 FUNCTIONS OF THE NERVOUS SYSTEM. 



430. Thus the analysis of such of the actions of these animals, as are evi- 

 dently of a higher order than the simply-reflex, terminates in referring them to 

 the immediate directing influence of Sensations ; which, being received by the 

 cephalic ganglia through the sensory nerves, excite respondent motor impulses, 

 which are propagated to the various muscles of the body, through those por- 

 tions of the motor trunks that issue from them. As the term Instinctive has 

 been employed in a great variety of significations, and is very indefinite in its 

 character, we may more appropriately apply the designation Consensual to the 

 actions of this group. We have now to inquire, whether there is any class of 

 movements in Man and the higher Vertebrata, which seems to possess a simi- 

 lar character, and which may be regarded as the special function of the gangli- 

 onic centres under consideration. By far the larger part of the movements of 

 these animals (putting aside the simply-reflex) are performed under the direc- 

 tion of the Intelligence ; to which the sensations are communicated ; by which 

 a reasoning process is founded upon them ; and from which, at last, issues 

 that mandate, which is called the Will. Consequently, there are compara- 

 tively few movements, in the adult at least, which can be clearly distinguished 

 as neither voluntary, on the one hand, nor reflex on the other. Such actions, 

 however, do exist ; and serve to show that, although the Instinctive propensities 

 are in great measure superseded by the Intelligence, they may still operate 

 independently of it. As examples of this group, we may advert to the act of 

 Vomiting, produced by various causes which act through the organs of sense; 

 such as the sight of a loathsome object, a disagreeable smell, or a nauseous 

 taste. The excitement of the act of Sneezing by a dazzling light, is another 

 example of the same kind; for even if it be granted, that the act of sneezing 

 is ordinarily excited through the reflex system alone (which is by no means 

 certain), there can be no doubt that in this instance it cannot be brought into 

 play without a sensation actually felt. The same may be said of the Laughter 

 which sometimes involuntarily bursts forth, at the provocation of some sight 

 or sound, to which no distinct ludicrous idea or emotion can be attached ; and 

 of that resulting from the act of tickling, in which case it is most certainly 

 occasioned by the sensation, and by that alone. 



431. The direct influence of Sensations, in occasioning and governing move- 

 ments, which are neither reflex nor voluntary, is most remarkably manifested 

 in many phenomena of disease. Thus in cases of excessive irritation of the 

 retina, which renders the eye most painfully sensitive to even a feeble amount 

 of light, the state designated as photophobia, the eyelids are drawn together 

 spasmodically, with such force as to resist very powerful efforts to open them ; 

 and if they be forcibly drawn apart, the pupil is frequently rolled beneath the 

 upper lid (apparently by the action of the inferior oblique muscle), much fur- 

 ther than it could be carried by a voluntary effort. And in Pleuritis, Pericar- 

 ditis, and other painful affections of the parietes of the chest, we may observe 

 the usual movements of the ribs to be very much abridged ; the dependence of 

 this abridgement upon the painful sensation which they occasion, being most 

 evident in those instances in which the affection is confined to one side, for 

 there is then a marked curtailment in its movements, whilst those of the other 

 side may take place as usual ; a difference which cannot be reflex, and which 

 the Will cannot imitate. Again, in some Convulsive disorders, we observe 

 that the paroxysms are excited by causes, which act through the organs of 

 special sense ; thus in Hydrophobia, we observe the immediate influence of 

 the sight or the sound of liquids, and of the slightest currents of air ; and in 

 many Hysteric subjects, the sight of a paroxysm in another individual is the 

 most certain means of inducing it in themselves. 



432. The results of experiments, so far as any reliance can be placed upon 

 them, confirm these views ; by showing that any disturbance of the usual 



