Whether or not such average values can be of practical use depends on how much the values vary with regard to individual infants and to single days or weeks of life. A complete agreement of the individual case with the famous average values hardly ever occurs in the infant, either in observation or in the calculation of probabilities.
The great majority of cases do not deviate widely from the average values. When constant influences are at work, such as the restlessness produced in the infant in the direct metabolism experiment, the devia tions from the normal may be such that they must be taken into consid eration. Careful observers have always noted these conditions, inas much as certain cases have been regarded as comparable while others were excluded front the comparison. For instance, an infant perspiring profusely, for some reason or other cannot be expected to void the same amount of urine as another infant not otherwise differing from the first under normal conditions of life. Or if an infant ten weeks old receives only GOO Gm. (21 ounces) of breast-milk instead of the normal amount of SilO Gm. (2s ounces), and its weight, owing to general debility, is only -1.4 kg. (10 lbs.) instead of the normal 5 kg. (11 lbs.), these two cir cumstances have a marked influence on the functions of its metabolism, which must be taken into consideration in comparing the metabolism with that of a normal infant. If a comparison is desired, the amount of food required in the given case would approach the amount for an infant of seven weeks rather than that for one of ten weeks, etc.
11y wily of explanation, two complete balances of metabolism and energy of infants in the tenth week of life may he cited. The average values of Lnlant 1 were obtained by the statistical method, the figures for Infant 2 are taken from the first experiment of Heulmer and Rubner, which lasted nine whole days-24-hour periods. The amount of food in Case 2 was insufficient, and the infant showed a tendency to diarrhcea. The following values were used for the calculation in Case living under normal conditions: Weight 5 kg., daily gain 25 Gin., with 3.7 Gm. proteid, containing ash and 3.3 Gm. fat. The so-called extractive substances, like glycogen, lecithin, etc., cannot be considered in such calculations, and their amount is only small. The daily food is taken to 800 Gin. breast-milk, with 7.6 G HI. proteid, 2ti Gm. fat, and .56 Gun. lactose. All other figures can be seen in the table. Infant 2 weighed at
the beginning of the experiment 5220 Gm., and at the end 5250 Gin., the average was taken as 5230 Gm. It drank daily 613 Gm. mother's milk, with 6.15 Gun. proteid, 17.1 Gm. fat, and -1:1.5 Gm. lactose. These figures and those of the following table were obtained by special analyses. The mother of the infant thought that the flesh of the baby had become more flabby than usual and the authors indicate that this observation was correct. On :termini of the insufficient nourishment, the calcula tion of the balance of energy showed a slight deficit.
Explanation of Infant 1.—The :36.4 Gnu. carbon of column (j) re quired for oxidation 102.5 Gm. oxygen; the 5.7 Gun. hydrogen required 45.6 Gm. oxygen; together 118.1 Gm. oxygen. From the ingested milk only :34.1 Gni. remained; therefore, 114 Gm. oxygen must be taken up through the respiration. The respiration excretes 140.9 Gm. carlion dioxide, and the skin and lungs excrete 20S.1 Gun. water, 51.3 Gm. of which are produced in the body through oxidation and 156.S Gm. come from the ingested milk. The loss through the gaseous metabolism (the so-called insensible perspiration) is 114—(140.9 208.1) = 235 Gm.
Explanation of Infant 2.—From 31.9 Gm. carbon and S5.0 Gm. oxygen and from 4.8 Gm. hydrogen and 38.2 Gm. oxygen, 116.9 Gin. carbon dioxide and 43.0 Gm. water are produced in the body through oxidation. Since carbon and hydrogen were derived from the organic substance, the carbon dioxide, the newly formed water, and the oxygen of the respiration had to be registered on the line of the organic sub stance. The 224.4 Gm. water eliminated through the skin and lungs are derived from 43.0 Gm. produced in the body and 181.4 Gin. of the milk. The insensible perspiration is 96.2—(116.9 + 224.4) = 245 Cm.
Balance 2 is more difficult to explain than is Balance 1 on account of the existing anomalies, the insufficient nourishment, and the excessive elimination of water vapor. Much crying caused a great loss of water vapor through the lungs, and the abnormally high temperature in the apparatus (about 25° C.; 77° F.) caused the loss through the skin. In spite of the small amount of milk taken in Case 2, the excretions through feces and the gaseous excretions do not differ very materially from those of Case 1 (20 Gm. as against 3S Gm., and 349 Gm. as against 3•1 Gin.). A considerable difference in regard to the excretion of urine is noted (520 Gm. as against 325 Gm.).