406 THE NUTRITION OF THE BABE. [BOOK iv. 



the whole circuit of the blood system is traversed in a shorter 

 time than in the adult (12 seconds as against 22) ; and conse- 

 quently the renewal of the blood in the tissues is exceedingly 

 rapid. Relatively to the body-weight there is also considerably 

 more blood in the babe than in the adult. 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 

 absorption of oxygen is said to be during these earlier years 

 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 (cf. 358). 

 This, indeed, is the striking feature of infant metabolism. It is a 

 metabolism directed largely to constructive ends. The food taken 

 represents, undoubtedly, so much potential energy ; but before 

 that energy can assume a vital mode, the food must be converted 

 into tissue ; and, in such a conversion, morphological and mole- 

 cular, a large amount of energy must be expended. The metabolic 

 activities of the infant are more pronounced than those of the 

 adult, for the sake, not so much of energies which are spent on 

 the world without, as of energies which are for a while buried 

 in the rapidly increasing mass of flesh. Thus the infant requires 

 over and above the wants of the man, not only an income of 

 energy corresponding to the energy of the flesh actually laid on, 

 but also an income corresponding to the energy used up in 

 making that living sculptured flesh out of the dead amorphous 

 proteids, fats, carbohydrates and salts, which serve as food. Over 

 and above this, the infant needs a more rapid metabolism to keep 

 up the normal bodily temperature This, which is no less, indeed 

 slightly (-3) higher, than that of the adult, requires a greater 

 expenditure, inasmuch as the infant with its relatively far larger 

 surface, and its extremely vascular skin, loses heat to a propor- 

 tionately much greater degree than- does the grown-up man. It 

 is a matter of common experience that children are more affected 

 by cold than are adults. The bodily temperature is moreover less 

 stable in the infant than in the adult, and departures from the 

 normal temperature have not the grave significance they have in 

 the adult. 



This rapid metabolism is however not manifest immediately 

 upon birth. During the first few days, corresponding to the loss 

 of weight mentioned above, the respiratory activities of the tissues 

 are feeble; the embryonic habits seem as yet not to have been 

 completely thrown off, and, as was stated in 376, new-born 

 animals bear with impunity a deprivation of oxygen, which would 

 be fatal to them later on in life. 



Associated probably with these constructive labours of the 



