856 THE PHASES OF LIFE. 



tity of undigested food (fat, casein, etc.), unaltered bile-pigment, and unde- 

 composed bile-salts. 



804. The heart of the babe (see Table, p. 855) 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 on- 

 ward. The respiratory work, while it increases absolutely as the body 

 grows, is, relatively to the body-weight, greatest in the earlier years. It 

 fs worthy of notice that the absorption 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. 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 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 re- 

 quires, 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 metab- 

 olism to keep up the normal bodily temperature. This, which is no less, 

 indeed, slightly (0.3) higher, than that of the adult, requires a greater ex- 

 penditure, 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. 305, newborn animals bear with impunity a deprivation of oxygen 

 which would be fatal to them later on in life. 



805. 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 secreted, 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. 



806. Associated probably with these constructive labors of the growing 



