AGE. 



65 



bers; but the only rational principle on which 

 we can distinguish certain definite periods, 

 must be that of observing alterations in the 

 condition of the whole body or of its several 

 organs, and the correspondence which they 

 bear to particular epochs. The old Aristo- 

 telian division of human life into three stages, 

 growth, maturity, and decline, is founded on 

 this principle ; for, viewing man as a whole, 

 the conditions in which he is an imperfect, a 

 complete, or a declining member of his species, 

 are well marked. But these conditions are 

 capable of subdivision according to the changes 

 which particular organs have undergone ; in 

 other words, man, in the progress of his per- 

 J'ectiomiement, makes certain acquisitions in his 

 structures and functions, and in his decline 

 suffers certain losses and impairments ; the 

 more striking of these additions to, or sub- 

 tractions from his resources, suggest the well- 

 known division of existence into infancy, boy- 

 hood, puberty or adolescence, manhood, old 

 age, and decrepitude. It is not our intention 

 to discuss the subject of age by describing the 

 characteristics of the stages last enumerated ; 

 we think it better to take a view of the general 

 revolutions which transpire in the human 

 economy during growth, maturity, and decline, 

 and under each of these heads to mention the 

 changes which particular organs undergo in the 

 course of time, without limiting ourselves to 

 distinct stages, the determination of which must 

 be, to a certain extent, arbitrary. 



The consideration of the alterations which 

 take place in the body during its progress from 

 infancy to manhood might very properly be 

 preceded by some remarks on those ultimate 

 processes which are essential to growth, viz. 

 nutrition, secretion and absorption ; but, for 

 information upon this interesting subject, the 

 limits prescribed to this article compel us to re- 

 fer the reader to that upon NUTRITION, in which 

 the processes alluded to will be viewed in rela- 

 tion not only to the development, but also to 

 the maintenance, and to the decay of the 

 tissues. 



On comparing a young with an adult animal 

 we are at first struck by the difference in bulk ; 

 but immediately afterwards our attention is 

 attracted by the difference in their respective 

 capabilities of action, a difference not merely 

 proportionate to that of size. A closer ex- 

 amination informs us, that in the infant many of 

 the parts of the body are absolutely incomplete, 

 as organs or instruments, and we proceed to in- 

 vestigate whether this imperfection holds with 

 all the organs or only with some of them; and 

 if the latter be the case, whether the parts thus 

 existing only in a rudimentary state belong to 

 ' a particular class. Now, the organs and func- 

 'ions of man, in common with those of other 

 animals, are divided into those which he shares 

 with organic beings in general, and those 

 which distinguish him as an animal ; the former 

 subserving hi s own independent existence, the 

 latter his existence in relation to external ob- 

 jects of his consciousness ; these more or less 

 subjected to the control of volition, those re- 

 moved, under ordinary circumstances, from the 



VOL. i. 



government of this principle. Hence these two 

 classes have been variously named organic 

 and animal, nutritive and relative, automatic 

 and voluntary ; and, as life is a term employed 

 to designate the collective functions according 

 to some physiologists, or the cause of them ac- 

 cording to others, we have organic life and 

 animal life, &c., &c. But the animal functions 

 are truly supplemental ; they could not subsist 

 but by virtue of the organic ; while, on the 

 other hand, the latter are perfectly capable of 

 a separate existence, as in the vegetable world, 

 or in those conditions of animal life in which 

 its characteristics are all but suspended, such 

 as profound sleep and apoplexy. Yet, al- 

 though the functions of relation are thus de- 

 pendent on those of nutrition, it is evident, at a 

 moment's glance, that the latter viewed col- 

 lectively in an animal structure, would present 

 an aspect altogether incomplete, and different 

 from that which we notice in the system of a 

 vegetable. In the one case they were obviously 

 intended to act only for themselves and for one 

 another ; in the other they have an ulterior 

 object to fulfil, but for which they would 

 not have been called into existence and opera- 

 tion; this object is the production and support 

 of the functions that constitute the animal. 

 If we now look at the new-born infant in con- 

 trast with the full-grown man, we at once per- 

 ceive that the essential difference between them 

 has reference to the life of relations ; in other 

 words, the immaturity of the former is not de- 

 termined by the state of the vegetative organs, 

 which, as organs, are perfect, but by the unde- 

 veloped conditions of the parts which are to 

 receive impressions from, and to re-act upon 

 surrounding objects. Thus, on the one hand, 

 we observe that the food adapted to the little 

 being is rapidly converted into chyle, that 

 the blood, after undergoing its requisite changes, 

 performs its circuit freely and effectively, and 

 that the activity of the nutritive, secernent, and 

 absorbent processes is evidenced by the quick 

 increase of growth, and by the abundant fluids 

 contained in the various tissues. But, on 

 turning to the relative functions, we find the 

 case altogether reversed ; sensation is dull, faint, 

 and flitting ; voluntary motion scarcely ex- 

 ceeds the amount necessary for obtaining nutri- 

 ment from the parent ; while the demonstra- 

 tions of intelligence are the very lowest com- 

 patible with our belief in the possession of 

 such a principle by the being in question. An 

 examination of the organs devoted to these 

 several actions leads to results in accordance 

 with what we observe in the functions them- 

 selves ; in the one class the organization is 

 complete, in the other much remains to be 

 accomplished. If the apparatus of digestion 

 be inspected, the parts employed in deglutition, 

 viz., the tongue, pharynx, and oesophagus, will 

 be found fully formed ; in the stomach the 

 parts required for accommodating the aliment 

 during its stay and for mixing certain fluids 

 with it, are properly developed ; no deficiency 

 is observable in the structure of the liver 

 and pancreas ; and the chyliferous vessels are 

 pervious, extensile, and perhaps contractile. If 



F 



