80 



AGE. 



mals is much less easily affected by reagents 

 than that of younger ones ; so that there would 

 appear to be an alteration in the chemical 

 composition as well as in the mechanical con- 

 sistence. 



That which has been said of the matter of 

 the nerves is also true of the brain. The 

 whole bulk is diminished arid the density 

 greater than in earlier years. Some, however, 

 assert that it is even softer than in manhood. 

 M. Blandin makes a remark of this kind, 

 in commenting upon Bichat's statement of a 

 greater hardness in the tissue, and says that 

 it might be expected a priori, since there is so 

 strong a correspondence between the two ex- 

 tremes of life. There is reason, however, to 

 think that this remark, if true at all, applies 

 only to the cerebral organ of persons very far 

 advanced ; and it is not improbable that dis- 

 eased softening has in other cases been mis- 

 taken for the natural effect of age. The mem- 

 branes investing the brain like the neurilemmes 

 (for they belong to the same system) are also 

 thicker and more resistent. The vascularity 

 of the organ is greatly diminished ; on a di- 

 vided surface no red dots are visible as at 

 periods less advanced. 



The alterations in the mechanism of the 

 senses must next be considered. The skin, 

 which is the medium between the nerves of 

 tact, and external agents, undergoes great 

 changes in the progress of life. It becomes 

 drier, harder, less flexible, and at the same 

 time looser, in consequence of the absorp- 

 tion of the adipose substance. By the latter 

 qualities the function of the skin is more 

 evidently impaired, in that modification of it 

 more expressly denominated touch, or the 

 sense of tact united with certain muscular 

 feelings in the fingers and hands. By the 

 looseness of the integuments, the slowness and 

 weakness of the muscles, the stiffness of the 

 digital joints, and that dulness of sensation 

 which exists in this as in every other part of the 

 system more or less, the hand is notably 

 deteriorated in old age. 



In the olfactory apparatus we find that, 

 although the cavities and sinuses, through 

 which the Schneiderian membrane is ex- 

 tended, are rather increased than diminished 

 in size, the membrane itself is attenuated and 

 less pulpy. The nerve also is mentioned by 

 Rulher* to be evidently contracted and wasted. 

 The sense of taste so closely connected with 

 that just spoken of survives to the extremes! limit 

 of existence ; the final cause of which is evi- 

 dent. It is too intimately connected with one 

 of the processes of organic life to be easily 

 dispensed with, although one of the functions 

 of the superadded life. It is, however, feebler 

 than at periods less advanced, and requires 

 the excitement of more piquant aliment ; this 

 is partly owing to the diminished sensibility 

 of the gustatory nerve itself, and partly to the 

 diminution of the sense of smell, on the per- 

 fection of which depends our appreciation of 

 the more delicate species of sapidity. The 



* Diet, de Med. art. Aye. 



surface of the tongue is more rugose than in 

 younger subjects, and there is generally a de- 

 ficiency of moisture, which is an additional 

 cause of diminished sensation. 



The ear, both in its external appendages 

 and in its internal structure, presents certain 

 conditions which very well account for the 

 frequency of deafness among the aged. It is 

 true the cartilages become harder, more elastic, 

 and therefore more vibratory, but the internal 

 surface of the meatus is often thickened, and 

 obstructed by a dense cerumen. The mem- 

 brana tympani is more rigid and therefore less 

 capable of varying with the degree of the vibra- 

 tions. In the internal cavity, although the 

 mastoid cells are enlarged as life advances, 

 the deficiency of the liquor cotunnii in the 

 vestibule, the cochlea, and the semicircular 

 canals, must greatly interfere with the produc- 

 tion of hearing. In addition to all these cir- 

 cumstances there is probably an idiopathic 

 insensibility of the nerve. 



The modifications of the organ of vision are 

 familiar to all who have paid even the most 

 superficial attention to the science of optics. 

 The cornea is less transparent and less convex, 

 partly from the diminution of the aqueous 

 humour, and partly from the condensation of 

 its texture. The latter change is more marked 

 at the circumference, where a nebulosity is 

 often formed, which has gotten the name of 

 gerontotoxon, or arcus senilis. The pigmentum 

 diminishes, and the iris grows paler in con- 

 formity with the altered colour of the hair. 

 The crystalline lens is denser, less transparent, 

 and often acquires a yellow tint ; the vitreous 

 hufnour likewise suffers a decrease. The retina 

 is considerably attenuated, but has increased in 

 firmness. The punctum luteum is paler, and 

 not unfrequently altogether effaced ; a change 

 which, in the opinion of Meckel,* bears a direct 

 ratio to the diminution of the transparency of 

 the cornea. These several .alterations are ne- 

 cessarily followed by two results diminished 

 refraction of the rays of light, and torpor of the 

 nervous function, both of which prod uce pres- 

 byopia. That long sight bears a relation with 

 nervous as well as more mechanical causes is, 

 we think, attested by the fact that this kind of 

 vision is modified by temporary excitement of 

 the brain, as in phrenitis.f 



If we now take a retrospect of the revolu- 

 tions which have occurred in the several struc- 

 tures enumerated, and endeavour to arrange 

 them under specific heads, it will be found 

 that diminution of bulk, deficiency of fluid, 

 and condensation of substance, comprehend 

 them all or nearly all. The attenuatjon has 

 been generally ascribed to a preponderance of 

 absorption over deposition, or a reverse of that 

 condition in which incremental growth consists. 

 But we cannot enter upon the question here, 

 and must refer to the article NUTRITION, con- 

 tenting ourselves with the remark that it seems 

 a superfluous multiplication of causes to sup- 



* Op. cit. t. iii. p. 261. 



t See Abercrombie on Diseases of the Brain. 



