106 GASEOUS METABOLISM OF INFANTS. 



Our chief aim, therefore, was to study the metabolism of normal 

 infants under conditions approximating the ideal, these infants to be 

 selected, first, with varying ages; second, with varying weights; and 

 third, of both sexes. That a sufficient number of observations could 

 be made in one or two years to establish a standard for the normal 

 metabolism of infants was hardly to be expected, but we at least hoped 

 to make a good beginning, knowing that in subsequent years our data 

 would be supplemented 1 and our findings from time to time revised. 



Perhaps the most important abstract problem which is met with in 

 an investigation of this nature— a problem interesting alike to both 

 physiologists and pediatricians— is the cause of the variations in the 

 metabolism of the infant. For instance, is the metabolism proportional 

 to the active mass of protoplasmic tissue? There is clearly a suggested 

 relationship between the metabolism and the body-weight, but the 

 metabolism per kilogram of body-weight is by no means an index of 

 the mass of active protoplasmic tissue; nevertheless some relationship 

 should exist. At present we are wholly unable to determine the total 

 mass of the active protoplasmic tissue in an infant's body. Unques- 

 tionably much of the gain in weight of a growing infant is due to the 

 storage of fat; it is likewise certain that the gain in weight due to the 

 nitrogen retained may not all be due to the formation of active proto- 

 plasmic tissue; thus the problem is doubly complicated. 



We may further ask "Is the metabolism proportional to the body- 

 surface?" Such a stimulating suggestion has been made by Rubner, 

 who computed in his earlier experiments the relationship between body- 

 surface and heat-production, finding it to be relatively constant for prac- 

 tically all species of warm-blooded animals, ranging in size from a horse 

 to a mouse. In round numbers Rubner finds this relationship to be not 

 far from 1 ,000 large calories per square meter of body-surface per 24 hours. 

 To throw light upon the important physiological problem of the relation- 

 ship between the body area and the total metabolism was one of our 

 main problems. 



PULSE-RATE. 



Very little attention has been paid to the normal pulse-rate of infants, 

 so that only such general statements as the following from Holt 2 are 

 found in the text books: 



"The pulse in early life is not only more frequent but it is very much more 

 variable than in adults. The following is the average pulse-rate of healthy 

 children during sleep or perfect quiet: 



6 to 12 months, 105 t o 115 per minute; 2 to 6 years, 90 to 105 per minute. 



*As our page proof goes to press, we are informed that Hoobler and Murlin have very recently 

 duplicated some of our experiments and although their observations include but two atrophic 

 infants, they report that their findings are in full accord with ours. Their results were reported 

 under the title "The energy metabolism of normal and marasmic children" at the fifty-eighth 

 meeting of the Society for Experimental Biology and Medicine, in New York, April 15, 1914, 

 and also at a meeting of the Inter-Urban Club, New York, April 17, 1914. 



2 Holt, Diseases of infancy and childhood, New York and London, 1911, p. 565. 



