150 OF THE STRUCTURAL ELEMENTS OF THE HUMAN BODY. 



129. From the time of its entrance into the world, however, the condition of 

 the Human infant is essentially changed. It is no longer supplied with nutri- 

 ment by the direct transmission of organizable materials from the circulating 

 fluid of the mother to its own ; but obtains it by the processes of digestion, ab- 

 sorption, and assimilation, which involve a certain expenditure of vital force in 

 the performance of the chemical and vital changes in which these processes con- 

 sist. Thus the secretion of the gastric, biliary, and pancreatic fluids is a truly 

 vital process, although the action of these fluids upon the alimentary materials 

 may be purely chemical ; so, again, although part of the process of absorption 

 is effected by purely physical agencies, another part involves the development 

 and active agency of cells, and thus occasions a demand for vital force ; and the 

 further preparation of the absorbed materials for the purposes of nutrition seems 

 also to require an expenditure of that which, for the sake of convenience, we 

 have termed the "cell-force." Thus, then, even as regards these preliminary 

 operations, the infant is placed in a very different condition from the intra-ute- 

 rine embryo ; and in order that the change may not be too sudden, the nutri- 

 ment provided by Nature for the early period of infantile life is such as to 

 occasion the least possible demand upon its vital powers for the preparation of 

 the organizable material which is required for its further growth and develop- 

 ment. But the transition is a most important one in another particular ; the 

 infant is now thrown in great degree upon its own resources for the generation 

 of its heat ; and this it is enabled to accomplish by the combustion of a portion 

 of its food which is specially provided for the purpose, this combustion being 

 promoted by the arrangements for that active respiration which now supersedes 

 the very limited aeration of its circulating fluids that was sufficient during foetal 

 life. Now in the movements of the respiratory muscles and of the walls of the 

 alimentary canal, we have a new source of expenditure of vital force, and of 

 destruction of tissue; and this expenditure is progressively augmented, as the 

 motions of the body and limbs become increasingly active. Thus we find that 

 the formative powers are not exercised during childhood and youth, solely in 

 the construction and augmentation of the fabric (as they were during embryonic 

 life), since there is a constant demand upon them for its maintenance ; and this 

 demand becomes greater and greater, in proportion to the exercise of the Animal 

 powers. 



130. At the same time there appears to be a progressive reduction in the 

 " germinal capacity ;" for not only is there to be observed a diminishing aptitude 

 for the production of new parts (as shown, for example, in the cessation of the 

 production of new tooth-sacs by gemmation from the old, the last operation of 

 this kind being that by which the "dentes sapientise" are originated ( 285)), 

 but we also perceive a decrease in the power of repairing the ravages which 

 disease or injury may have made in the organism as previously formed. Still, 

 however, this capacity manifests itself in a very remarkable manner during the 

 whole period of growth ; being most obviously displayed in the complete evolu- 

 tion of the generative apparatus, the condition of which was previously rudiment- 

 ary ; but being in reality yet more remarkably exhibited in the various acts by 

 which the type or pattern of the organism is maintained and completed, not- 

 withstanding the various influences tending to its degradation. For it must be 

 borne in mind, that the growth of the body of Man, or of that of any of the 

 higher Animals, takes place in a manner essentially different from that of the 

 Vegetable fabric ; the latter mainly consisting in addition to the parts already 

 formed, whilst the former is effected by a continual development of new structure 

 in place of the old. Thus in the Tree we observe, year by year, the same trunk, 

 the same branches, the same roots ; and the only difference which we notice 

 between the young tree and the old one consists in the increased thickness of 

 the original stem and of its ramifications, which is shown by a transverse section 



