AGE. 



77 



do not hesitate to consider them mature; we 

 must therefore infer that there is a correspond- 

 ing organic development of some kind in the 

 cerebral substance. Maturity then would, ac- 

 cording to this view, require to be dated at a 

 period much later than that which is usually 

 assigned to it. It is enough, however, without 

 referring further, to know that although at the 

 adult period the organs of animal life are so 

 developed, that we cannot consider them im- 

 perfect instruments, they are even afterwards 

 the subjects of a perfect ionnement. What is 

 commonly meant then by maturity, is in strict- 

 ness that period of human existence, during 

 which the processes of growth and decline are 

 passing into each other by such slow degrees 

 as to be imperceptible. 



In this important era of the life of man, 

 more important even than the season of adole- 

 scence, we must leave him in the full posses- 

 sion of all the faculties and energies which his 

 Maker has allotted him, fulfilling his destiny of 

 good and evil, encountering and triumphing 

 over peril, toil, and pain, scaling the rough 

 steep of ambition, threading the dark intricate 

 paths of gain, labouring for the happiness or 

 misery of his fellow-creatures, supported all 

 the while by the consciousness of a strength 

 that seems never to fail him, of resources never 

 to be exhausted ; we must allow a few years to 

 roll by, and then return to him, when weary, 

 wayworn, and broken with the storms of life, 

 he has discovered that there are limits to his 

 powers of action and endurance ; that of the 

 objects which he proposed as the ends of his 

 labours, while a few have been accomplished, 

 the majority are either vain or unattainable ; 

 and that a race fresh in vigour, and high in 

 hope, the images of his former self, are over- 

 taking and thrusting him away from the scenes 

 of his exertions. What are the revolutions 

 that have transpired in his system ? 



The formative organs of all the tissues of 

 the body are in reality the tissues themselves ; 

 whether it be a muscle, or a gland, or the coat 

 of a vessel, the parts which essentially produce 

 its growth are nothing more or less than its 

 own constituent molecules, the mutual attrac- 

 tions of which in deposition and absorption 

 constitute assimilation ; for there is no proof 

 that vessels are used for any other purpose 

 than that of conveying the nutrient fluids to 

 and from the places, where the ultimate mole- 

 cules arrange themselves in the form of tissue. 

 The altered qualities, then, which are presented 

 by the tissues, in whatever organs, in the de- 

 cline of life, must depend immediately upon 

 alterations in their own molecular motions 

 and affinities. The nature of these alterations 

 will of course correspond to the nature of each 

 tissue ; and unless we mistake, they will all 

 be found to agree in one character, viz. a sim- 

 pler composition, a lower kind of organization 

 than they formerly possessed. But the discussion 

 of this point will be more conveniently deferred 

 till we shall have briefly recited the principal 

 changes in the more important parts of the 

 body. 



As the nutritive secretions of the various 



structures are supplied with materials by the 

 fluids in those structures, it is evident that they 

 must at any time be increased, diminished, or 

 otherwise modified by changes in the quantity 

 and properties of these fluids. It is therefore 

 a natural commencement of the subject to begin 

 with the circulating system. 



Nothing is more obvious in the condition of 

 the aged as contrasted with the young than the 

 different ratio between the fluids and the solids, 

 the former being remarkably deficient. There 

 is not only a notable diminution in the quantity 

 of oleaginous or serous secretions, which are 

 generally contained in the cellular parts of the 

 body, but it is manifest that the tissues are per- 

 meated by a much smaller proportion of blood. 

 This fluid moreover is very different in quality 

 from what it was in earlier life ; it is less arte- 

 rial, its colour has not the same bright red it 

 once presented, it has a large proportion of 

 serum, and its coagulum is less firm in con- 

 sistence.* Correspondently with the defi- 

 ciency of fluids, many parts which once 

 contained them are shrunk or obliterated. The 

 capillary system becomes infinitely less ex- 

 tended than it once was ; many of the extreme 

 branches of the arteries themselves are no longer 

 to be penetrated, and those which remain per- 

 vious, are far less distensible than formerly. 

 There is indeed a remarkable change in the 

 coats of these vessels ; they are not only con- 

 tracted in diameter, but are become denser and 

 more rigid in texture. In this respect they dif- 

 fer from the veins, which in old age are more 

 dilatable than in youth, and consequently con- 

 tain a larger quantity of blood. The final 

 cause of this is evident ; in youth the arteries 

 must convey a relatively larger quantity to sup- 

 ply the increasing structures; in the decline of 

 life, when the latter are decreasing, there can no 

 longer be any need for the same supply; 

 the permission, however, of an accumulation in 

 the veins, where it is less likely to be productive 

 of injury, appears to be an accommodation to 

 the diminution of the circulating powers. 



If we trace the arteries from their extremities 

 back to the heart, we shall find their calibres 

 every where diminished, their coats less elastic, 

 less capable of adapting themselves to the 

 varying quantity of their contents, in some 

 places resembling the texture of ligament, in 

 some that of cartilage, and in others studded 

 with deposits of osseous matter. The heart 

 itself presents marks of degeneration no less 

 decided ; its cavities are shrunk, its fibres pale, 

 and but feebly contractile, and fat will some- 

 times seem to take the place of the muscular 

 substance. Frequently, also, the coronary arte- 

 ries are found ossified, and the same alteration 

 is not uncommon in the valves. 



All these facts account for the slow, languid, 

 staggering circulation characteristic of advanced 

 life ; there is less blood to be transmitted to the 

 various organs, and that which is sent is pro- 

 pelled with a degree of feebleness that shows 

 how little energy is required in its motion, when 



* De Blainville is of opinion that these changes 

 are exaggerated. Cours tie Physiologie, i. 262. 



