686 CHILDHOOD. [BOOK iv. 



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 molecular, 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 amor- 

 phous 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 

 proportionately 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. 



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 on p. 377, new- born 

 animals bear with impunity a deprivation of oxygen, which would 

 be fatal to them later on in life. 



The quantity of urine passed, though scanty in the first two 

 days, rises rapidly at the end of the first week, and in youth the 

 quantity of urine passed is, relatively to the body-weight, larger 

 than in adult life. This may be, at least in quite early life, partly 

 due to the more liquid nature of the food, but is also in part the 

 result of the more active metabolism. For not only is the quantity 

 of urine passed, but also the amount of urea and some other 

 urinary constituents excreted, relatively to the body-weight, 

 greater in the child than in the adult. The presence of uric, of 

 oxalic, and according to some, of hippuric acids in unusual quantities 

 is a frequent characteristic of the urine of children. It is stated 

 that calcic phosphates, and indeed the phosphates generally, are 

 deficient, being retained in the body for the building up of the 

 osseous skeleton. 



Associated probably with these constructive labours of the 

 growing frame is the prominence of the lymphatic system. Not 

 only are the lymphatic glands largely developed and more active 

 (as is probably shewn by their tendency to disease in youth), but 

 the quantity of lymph circulation is greater than in later years. 

 Characteristic of youth is the size of the thymus body, which 



