AGE. 



73 



ness of touch, tactus eruditus, is one of the 

 most difficult attainments of manhood. 



Concerning the alterations in the olfactory 

 apparatus we have already spoken, when the 

 development of the facial bones was under 

 consideration. The sense of smell is mani- 

 fested pretty early, but there can be no great 

 precision and nicety in its exercise, both from 

 defect of surface, and from the want of mus- 

 cular power and command, in adjusting the 

 quantity and impetus of the air that conveys 

 the odorous particles. Thus, some agents are 

 only appreciated by a sudden inhalation through 

 the nostrils, as if to bring the particles with a 

 certain degree of force upon the Schneiderian 

 membrane. This art the child does not under- 

 stand. 



Taste being a sense so essential to the main- 

 tenance of the system, whether by inducing the 

 animal to take the trouble of eating, or by 

 warning him of improper aliment, is mani- 

 fested very early. The usual description of the 

 mechanism of taste would give just cause for 

 questioning what was said respecting the ne- 

 cessity of a co-operation of muscular action 

 with the five senses. Taste is described as 

 the result simply of the application of sapid 

 bodies to the tongue, palate, velum palati, &c. 

 But these bodies excite no sensation without 

 the aid ot muscles. A certain degree of com- 

 pression is necessary, which is accomplished 

 by pressing the tongue against the roof of the 

 mouth. Any one may assure himself of this fact 

 by placing a strongly flavoured substance on 

 the tongue when projected from the mouth; 

 no taste will ensue till the member is with- 

 drawn and then pressed against the palate. 

 This observation applies not only to the tongue 

 but also to the palate itself, and that sensitive 

 surface the velum. In each instance, however, 

 the effect may be imitated, by compressing 

 with the finger the part where the substance is 

 applied. 



Taste must undergo a progressive develop- 

 ment correspondently with the muscular or- 

 gans. It is, to say the least, very doubtful if 

 a child could perform those delicate manffiuvres 

 of the tongue and palate, which are practised 

 by gourmands or professed wine-tasters. There 

 is something more than this muscular action, 

 however, to be taken into consideration. The 

 more refined flavours are probably felt and 

 estimated by the lining membrane of the nasal 

 passages. It is common to remark that the 

 scent of a substance is similar to its taste, but 

 in all probability the two sensations are iden- 

 tical ; for the taste in question is not perceived 

 if the nostrils be closed ; witness the abolition 

 of taste during a catarrh. If therefore so close 

 a connection exists between the two senses, 

 it is clear that the development of the organi- 

 zation belonging to the one must influence the 

 other function ; and it has been already pointed 

 out that the olfactory surface increases with 

 growth. 



The new-born infant is probably all but deaf; 

 even the loudest sounds produce no sensible 

 impression. The nurse's lullaby, therefore, is 

 for some time superfluous ; by degrees, how- 



ever, the shrill tones, of which such strains for 

 the most part consist, begin to be appreciated ; 

 the precise period however we do not know. 

 In correspondence with this obtusity we find 

 the organ incomplete, but the incompleteness 

 has reference rather to the external than to the 

 internal ear. Thus the pinna is very inelastic, 

 and therefore unfitted for collecting vibrations ; 

 the same may be said of the meatus auditorius. 

 In like manner, the membrana tympani is very 

 oblique, and scarcely more than a continuation 

 of the superior surface of the meatus, and thus 

 little calculated to receive the vibrations. These 

 parts are also covered with a soft matter very 

 unfavourable to vibrations ; the tympanum is 

 very small, and the mastoid cells do not exist. 

 In the progress of age all these parts gradually 

 increase in hardness, and consequently are bet- 

 ter adapted to their function. There are mus- 

 cles attached to this sense also, but we are 

 deficient in observations on their degree of de- 

 velopment, though we may infer their condition 

 from analogies in the rest of the muscular 

 system. 



Lastly, we come to the organ of vision, of 

 which, however, there is not much to be said. 

 The differences between the visual organ in the in- 

 fant and in the adult consist more in degree than 

 in kind; thus the sclerotic membrane is less 

 elastic, and the cornea is less conical, in conse- 

 quence of the smaller quantity of aqueous hu- 

 mour; (the greater thickness of this coat is pro- 

 duced by the serosity contained between its la- 

 minae;) the crystalline lens is less dense, but more 

 convex in form. The pigmentum is in smaller 

 quantity at birth than afterwards ; while the retina 

 is thicker and more pulpy than in more ad- 

 vanced periods. The yellow tint of the foramen 

 of Soemmering does not become visible till 

 some time after birth, but deepens with the 

 progress of life, till the stage of decline, 

 when it grows paler. It has been ascertained 

 that perfect images are formed on the retina ; 

 and yet for the first few days the child gives no 

 indication of visual sensation, and when objects 

 appear to attract its attention, they are only 

 those which are vividly illuminated. The de- 

 ficiency therefore must exist in the optic nerve, 

 though we are ignorant of the organic condition 

 on which this insensibility is dependent. We 

 observe, moreover, that the eye is much more 

 passive than in the adult, that it follows the 

 motion of luminous bodies, or is fixed upon 

 them with little or no apparent interference of 

 the will. This muscular incompleteness, then, 

 tallies with what we have noticed with respect to 

 the other senses. The eye is known in its advance 

 towards manhood to increase in the capability 

 of adapting itself to different distances; but as 

 we are ignorant of the mechanism made use of 

 for this purpose, it is useless to look for cor- 

 responding organic alterations. We must not 

 omit to notice those appendages to the appara- 

 tus of vision, called eyebrows, which become 

 much more prominent as life advances, by the 

 development of the frontal sinuses, and are 

 therefore better adapted for shading the eyes. 



The generative apparatus is situated inter- 

 mediately to the animal and the organic system. 



