CHAP, v.] THE PHASES OF LIFE. 685 



and eye are concerned at least, has a morphological or phylogenic, 

 as well as a physiological or teleological, significance. Inasmuch 

 as the smaller body has relatively the larger surface, the skin is 

 naturally proportionately greater in the babe. It is chiefly by the 

 accumulation of muscle or flesh, properly so called, that the child 

 acquires the bulk and weight of the man, the skeletal framework, 

 in spite of its being specifically lighter in its earlier cartilaginous 

 condition, maintaining throughout life about the same relative 

 weight. 



The increase in stature is very rapid in early infancy, 

 proceeding however by decreasing increments. During or shortly 

 before puberty, there is again a somewhat sudden rise, with a 

 subsequent more steady but diminishing increase up to about 

 the twenty-fifth year. From thence to about fifty years of age the 

 height remains stationary, after which there may be a decrease, 

 especially in extreme old age. 



The increase in weight is also very rapid at first, and proceed- 

 ing, like the height, with diminishing increments, may continue 

 till about the fortieth year. After the sixtieth year a decline 

 of variable extent is generally witnessed. It is a remarkable 

 fact, however, that in the first few days of life, so far from 

 there being an increase, there is an actual decrease of weight, 

 so that, even on the seventh day the weight still continues to be 

 less than at birth. 



The saliva of the babe is active on starch, and its gastric juice, 

 unlike that of many new-born animals, has good peptic powers, 

 from which we may infer that its digestive processes in general are 

 identical with that of the adult ; but the faeces of the infant con- 

 tain, besides considerable quantity of undigested food (fat, casein 

 &c.), unaltered bile-pigment, and undecomposed bile-salts. 



The heart of the babe (see Table, p. 684) is, relatively to its 

 body-weight, larger than the adult, and the frequency of the heart-- 

 beat much greater, viz. about 130 or 140 per minute, falling to 

 about 110 in the second year, and about 90 in the tenth year. 

 Corresponding to the smaller bulk of the body, the whole circuit of 

 the blood system is traversed in a shorter time than in the adult 

 (12 seconds as against 22); and consequently the renewal of 

 the blood in the tissues is exceedingly rapid. The respiration of 

 the babe is quicker than that of the adult, being at first about 35 

 per minute, falling to 28 in the second year, to 26 in the fifth 

 year, and so onwards. The respiratory work, while it increases 

 absolutely as the body grows, is, relatively to the body-weight, 

 greatest in the earlier years. It is worthy of notice, that the ab- 

 sorption of oxygen is said to be relatively more active than the 

 production of carbonic acid ; that is to say, there is a continued 

 accumulation of capital in the form of a store of oxygen-holding 

 explosive compounds (see p. 349). This, indeed, is the striking 

 feature of infant metabolism. It is a metabolism directed largely 



