GENERAL SURVEY OF THE LIFE OF MAN. 151 



to depend entirely upon the enclosure of the original in new layers of wood pro- 

 gressively developed around it, and in the greater number and extent of the 

 smaller twigs and rootlets, which are put forth, year by year, from the larger. 

 When we compare, on the other hand, a single limb of the adult man with that 

 of the infant, we find that the position of every part of it has changed. The 

 same bones, muscles, tendons, ligaments, bloodvessels, nerves, &c., are recog- 

 nizable in both cases; and maintain, with little variation, the same relative po- 

 sitions. But the bone has swollen, as it were, in every direction, so that its 

 very cavity is now of absolutely larger diameter than the entire shaft of the 

 bone of the infant, whilst the whole length of the latter would constitute but a 

 fraction of the distance that now intervenes between its extremities. With the 

 enlargement of the bone, the points of muscular attachment are of course sepa- 

 rated from each other ; and the muscles themselves undergo a similar augment- 

 ation, as do likewise all the soft tissues connected with them ; these seeming, 

 like the bone, to have swollen by a process of interstitial growth, rather than 

 to have simply received additions to their surface and extremities. Now it will 

 be shown hereafter ( 267), that this enlargement is effected, in the case of the 

 Bone, not by a mere superficial addition (such as that which causes the shell of 

 the Echinus to swell from the size of the head of a pin to that of the head of a 

 child, the new matter being developed at the edges of the numerous polygonal 

 plates of which it is composed), but by a combination of the processes of absorp- 

 tion and of deposition ; or rather, in fact, by the continual progress of degene- 

 ration and death, consentaneously with every new production of living organized 

 tissue. And what is true of the bone is true also, there is good reason to be- 

 lieve, of the Muscles and all the softer organs, the normal duration of whose 

 individual parts is naturally less ; so that their enlargement seems essentially 

 to consist in the excess of production over the disintegration which is continually 

 taking place in them, this disintegration (as shown by the amount of the urea, 

 carbonic acid, &c., which are excreted) being far more rapid during the period 

 of growth than it is in the subsequent stages of life. 



131. That the germinal capacity, though inferior to that of the embryo, still 

 persists in a high degree during the period of childhood and youth, is further 

 shown in the readiness with which the effects of injuries and disease are recovered 

 from y for although the regeneration of lost parts does not take place to nearly 

 the same extent as during early embryonic life, yet, up to a certain point, it is 

 effected with great completeness, and with much greater rapidity than at later 

 epochs. It is still, in fact, rather in the exercise of formative power, than in 

 the production of nervo-muscular vigor, that the vital force of this period is 

 displayed ] and we may readily trace such a relation of reciprocity between these 

 two modes of its manifestation, as is strongly indicative of the community of 

 their source. For it is familiar to every observer, that, when the growth of a 

 child or a young person is peculiarly quick, its nervo-muscular energy is usually 

 feeble, and its power of endurance brief, in comparison with that which can be 

 put forth by one whose frame is undergoing less rapid increase. And we observe, 

 moreover, that the capacity of resistance to depressing influences of various kinds, 

 which is a no less decided manifestation of the vital power of the organism (see- 

 ing that these influences are of a kind which tend towards its death), is possessed 

 by the latter in a far higher degree than by the former. Under one form or 

 the other, however, we must recognize the existence of a high degree of vital 

 power during the period of childhood and adolescence ; and this power is sus- 

 tained by the large consumption of food; for this affords not merely the mate- 

 rials largely required for the construction of the fabric (which may be said to 

 bo in continual progress of pulling-down and rebuilding, all the old materials 

 being carried away as useless), but also those which serve for the maintenance 

 of the heat of the body, and which thus supply the force which is requisite for 



