upon diseased organs, being able also to cause the opposite effect of inducing unhealthy changes. 44. Associated differences in Sensations.-We have seen that discrimination is a fundamental property of the intellect, and that in so far as we can note differences in our sensations, to that extent these may be called intellectual. Even in Pleasure and Pain, the nice discrimination of more or less, or of one kind as compared with another kind, is an intellectual act. If one person is sensitive to a small difference in pleasurable or painful sensibility, such as would be unfelt by another person, the one may be said to be superior to the other intellectually. Discrimination is the groundwork of all knowledge; for to know things is to be impressed with their respective characteristic sensations or impressions. We should not know any human beings if they all impressed us alike. A botanist sees in a meadow twenty species of grasses; an ordinary person has perhaps remarked three or four. As discrimination extends, knowledge and all its consequences extend also. There is an important class of sensations that in themselves, or as originally felt, are precisely identical, but, by taking on different associations, become as distinct to the mind as sweet and sour in taste, acute and grave in sound, or red and green in colour. In the sense of Touch, for example, consider the two hands. If we compare the feeling of touch in the right hand with the same kind of contact in the left, we find that they are, as feelings, absolutely identical. But for intellectual purposes, they become quite distinct; they can sustain totally different associations. With a touch upon my left hand, I associate a whole field of imagery seen on my left side, and with a touch on my right hand, I associate another set of imagery in connexion with my right side. If any one pinches my right hand, I incline my head and direct my eyes right; if my left hand is pinched in precisely the sa her, my movements are all towards the left. em identical in everything but association. of suspending different associations proves ASSOCIATED DIFFERENCES IN MUSCULAR FEELINGS. 397 that there is a real difference in the sensations, that they are not confounded in the brain, though we may not trace this difference in the immediate consciousness. Association alone brings it out.* 45. The very same line of illustration can be followed with the muscular feelings. The feeling of a muscle under contraction has a uniform character all over the body, the degree of tension and all other circumstances being equal. Not to insist on the case of the two arms, or the two legs, or the rotation of the body in opposite ways, which would be similar to the foregoing illustration from touch, we can suppose a weight borne by the arm to give the same amount of muscular feeling as a pressure exerted by the foot, Under this supposition, two feelings are produced that have no difference, either as regards feeling, or as stimulating volition; yet experience shows that they are recognized as distinct by the mind. The two muscular tensions are made manifest to Our power of localizing our feelings of Touch and Sight has been explained differently. It is maintained in Germany by Lotze, Wundt, and others, upon the evidence of experiments, that the tactile sensations of the two hands, and of the skin everywhere, are qualitatively different, and that this difference of quality assists us greatly in learning to discriminate the several localities. To obviate the objection, from our not habitually recognizing any qualitative distinction in the touches in different parts of the body, it is remarked, no doubt with justice, that we are so much concerned habitually with the objective perceptions, as no longer to attend to the subjective differences. These differences may, nevertheless, at an early stage, have been sufficiently marked to form the basis of our local discriminations. In the case of Touch, the supporters of this doctrine find some difficulty in stating what is the kind of quality whose variation is perceptible over the body generally. But in Sight, there is no such difficulty. It is laid down, on the faith of experiment, that the sensibility of the eye is locally different to colour; for if we cause the same colour to pass from the yellow spot to the distant parts of the retina, it will appear, not the same, but different; and the variation of shade would thus be a mark of the place in the retina where the impression falls. We have here something definite to proceed upon. We can institute an inquiry, as to whether the discrimination of difference of shades of colour is sufficiently delicate, to correspond with the minuteness of vision formerly described. Some difficulty might be experienced, under such an hypothesis, in explaining how we should distinguish between an actual succession of colours the consciousness by different nerves; and, on this fact, the mind is able to build and maintain distinct associations, although not aware of any difference, either of quantity or of quality, in the feelings as such. We have already called attention to the articulate character of the sense of Touch, arising from the independence of the nerves of the skin, as distributed over the general surface, a remark applicable also to the nerves supplied to the different muscles. The same kind of feeling, coming from different parts, is recognized as different by taking on different associations. Before any associations are formed, the difference is latent; after the growth of distinctive connexions it is unmistakeable. The localizing of our feelings-the possibility of assigning a locality to each-is founded on this distinctness of the nerves arising from different parts. If a prick in the leg and a prick in the arm were as undistinguishable in every way, as they are to the mere sense of pain, we should never be and the same colour passing over different fibres. I do not say that this is an insuperable obstacle, if it could be shown that our ability to distinguish nice gradations of colour is such as to approach the observed limits of fineness of vision. Between the centre of the yellow spot, and a point in the retina, say 10° removed from it, we should require to interpolate, at the very least, several hundreds of shades of redness passing into green or blue. I am not prepared to affirm that this is impossible to the primitive eye; but it is hardly consistent with our ordinary estimate of the powers of the eye, even in persons educated to the discrimination of colours. Still, the hypothesis is one that deserves to be entertained; it is in some respects, perhaps, less difficult than the assumption of a sense of difference in feelings qualitatively identical, an assumption supported only by its being adequate to account for the facts of local discrimination. The supposition of latent qualitative differences, where to the common apprehension there is nothing but sameness, must, it would seem, be likewise extended to the muscles. It would have to be shown that there is something distinct in the muscular feelings of the two arms exerted exactly in the same way. When muscles are of very different magnitude and calibre, as the deltoid of the shoulder, the biceps of the arm, the diaphragm, and the orbicular muscle of the mouth, I can readily suppose that we should be differently affected by their contraction; the difficulty consists in assigning a characteristic peculiarity in the feeling of expended energy in two muscles in all respects resembling, as in those of the two sides of the body, and in others almost identical in size and in form. ASSOCIATED DISCRIMINATIONS IN THE RETINA. 399 able to connect the one with our notion of the leg, and the other with our notion of the arm, or with any of the other distinctive features of those two members. If not superfluous, after these examples, the eye might be adduced to the same effect. The place of the retina. impinged upon by a ray of light, is, in the main, unimportant as respects the feeling of light, but there is, notwithstanding, a real difference in the intellectual point of view, brought, out, as in the other cases, by association. We can thus discriminate right and left, up and down, centre and circumference, in our field of view, as soon as any characteristic actions, or consequences, become connected with the different portions of the retina impinged upon from these various outward positions of the rays of light. The retina is in this respect identical with the skin; it consists of a number of independent nerve fibres, each transmitting the same quality of impression (unless the theory of qualitative differences can be established), but to a distinct region of the common centre of visual impressions, and so as to form the starting point of a perfectly distinct series of accompanying impressions. A man at a telegraphic station, under the old system of signals, saw the same arm repeated to his view; but, with its picture on the lower part of the retina he connected one action, on the upper part another action. This is associated discrimination.* Sir William Hamilton's theory of the inverse relation between Sensation and Perception. This theory has been stated by its author as follows:Though a perception be only possible under condition of a sensation; still, above a certain limit the more intense the sensation or subjective consciousness, the more indistinct the perception or objective consciousness.' By the 'sensation' is here meant the feeling as regards pleasure or pain; by the perception' I understand what is termed above the intellectual discrimination; the difference is like that between the excitement of a blaze of sunshine and the discrimination of two natural history specimens. These two effects Sir William Hamilton believes to be inverse to one another; that is, in proportion as the one is strong the other is weak. I am disposed to admit the truth of this doctrine to a very considerable extent. But it appears to me that the facts as to the relation of these two qualities-the emotional on the one hand, and the intellectual on the other-show a greater degree of complexity than ASSOCIATES WITH FEELING. 46. The element of Feeling, or pleasure and pain, viewed as such, enters into alliance with the more intellectual states of mind, as, for example, those neutral perceptions of outward things that we have just been considering. This alliance or association between feeling and imagery gives rise to a number of interesting phenomena, some of which may be introduced here, as presenting a new case of the associating process. In the pleasures and pains derived through the various senses and through the moving organs, associations spring up with collateral things, the causes or frequent accompaniments this law expresses, even although it be correct as to the prevailing character of the relation. The following extract contains the statement of the facts adduced in support of this theory by its author. If we take a survey of the senses, we shall find, that exactly in proportion as each affords an idiopathic sensation more or less capable of being carried to an extreme either of pleasure or pain, does it afford, but in an inverse ratio, the condition of an objective perception more or less distinct. In the senses of Sight and Hearing, as contrasted with those of Taste and Smell the counter proportions are precise and manifest, and precisely as in animals these senses gain in their objective character as means of knowledge, do they lose in their subjective character as sources of pleasurable or painful sensations. To a dog, for instance, in whom the sense of smell is so acute, all odours seem, in themselves, to be indifferent. In Touch or Feeling the same analogy holds good, and within itself; for in this case, where the sense is diffused throughout the body, the subjective and objective vary in their proportions at different parts. The parts most subjectively sensible, those chiefly susceptible of pain and pleasure, furnish precisely the obtusest organs of touch; and the acutest organs of touch do not possess, if ever even that, more than an average amount of subjective sensibility.The experiments of Weber have shown, how differently in degree different parts of the skin possess the power of touch proper; this power, as measured by the smallness of the interval at which the blunted points of a pair of compasses, brought into contact with the skin, can be discriminated as double, varying from the twentieth of an English inch at the tip of the tongue, and a tenth on the volar surface of the third finger, to two inches and a half over the greater part of the neck, back, arms, and thighs. If these experiments be repeated with a pair of compasses not very obtuse, and capable, therefore, by a slight pressure, of exciting a sensation on the skin, it will be found, that whilst Weber's observations, as to the remarkable difference of the different |