CHAPTER I.
SENSATION.
“I shall not at present meddle with the physical consideration of the mind, or trouble myself to examine wherein its essence consists; or by what motions of our spirits, or alterations of our bodies, we come to have any Sensation by our organs, or any Ideas in our understandings; and whether those ideas do in their formation, any or all of them, depend on matter or no. These are speculations which, however curious and entertaining, I shall decline, as lying out of my way in the design I am now upon.”—Locke, i. 1, 2.
MY object, in what I shall say respecting the phenomena classed under the head of SENSATION, is, to lead such of my readers as are new to this species of inquiry to conceive the feelings distinctly. All men are familiar with them; but this very familiarity, as the mind runs easily from one well known object to another, is a reason why the boundary between them and other feelings is not always observed. It is necessary, therefore, that the learner should by practice acquire the habit of reflecting upon his Sensations, as a distinct class of feelings; and should be hence prepared to mark well the distinction between them and other states of mind, when he 3 advances to the analysis of the more mysterious phenomena.
What we commonly mean, when we use the terms Sensation or phenomena of Sensation, are the feelings which we have by the five senses,—SMELL, TASTE, HEARING, TOUCH, and SIGHT. These are the feelings from which we derive our notions of what we denominate the external world;—the things by which we are surrounded: that is, the antecedents of the most interesting consequents, in the whole series of feelings, which constitute our mental train, or existence.
The feelings, however, which belong to the five external Senses are not a full enumeration of the feelings which it seems proper to rank under the head of Sensations, and which must be considered as bearing an important part in those complicated phenomena, which it is our principal business, in this inquiry, to separate into their principal elements, and explain. Of these unnamed, and generally unregarded, Sensations, two principal classes may be distinguished:—first, Those which accompany the action of the several muscles of the body; and, secondly, Those which have their place in the Alimentary Canal.[1]
[1] Important points of Psychology are raised in classifying the senses, and in assigning the order of their exposition. The author justly animadverts on the insufficiency of the common enumeration of the Five Senses, and indicates two grand omissions—the Muscular Sensibilities, and the feelings associated with Digestion.
With regard to the first omission—the Muscular Feelings,—a further advance has been found requisite. Instead of adding these to the list, as a sixth sense, they are made a genus apart 4 and put in contrast to the Sensations as commonly understood. They are the feelings of our ACTIVITY, of the Active side of our nature, and are in relation to the Motor or Outcarrying nerves of the body. The Sensations proper, such as Smell and Hearing, are the feelings of our RECEPTIVITY, or Passivity, and arise in connection with the Sentient, or Incarrying nerves. In the exercise of the senses, however, a muscular element is almost always combined. This is conspicuous in Touch, which is most frequently accompanied with movements of the hand, or other parts touched; it is also the case with Sight, there being six muscles constantly engaged in moving the eye-ball. There is least muscularity in Hearing and Smell, but in neither is it wholly absent. Thus in Hearing, there are certain small muscles for adjusting the tightness of the membrane of the tympanum; apart from which, there are movements of the head in conjunction with hearing. So in Smell; the sniffing action with the breath is muscular. Nevertheless, it is easy to separate, in all the senses, the passive and proper sensibility of the sense, (called by Hamilton the idiopathic sensibility) from the active accompaniment. We can make experiments upon passive touch, or pure contact; we can isolate in our consciousness the optical sensibility of the eye; we can eliminate activity from the ear; and we can attend to the sensations of smell in their pure passivity.
The best course of proceeding is to deal with Muscularity apart, in the first instance, and to give it the priority in the order of exposition. Chronologically it is an earlier fact of our being; we move before we feel; there is an inborn energy of action in the animal system, which goes out, as it were, and meets the objects of sensation. This is one reason of priority. Another is the fact just stated that movement accompanies all the senses, or is a common factor in sensation. To discuss its peculiar sensibility is thus a preparation for treating of the senses.