BASIC PRINCIPLES. 23 



BASIC PRINCIPLES. 



Though Howland, using Lusk's calorimeter, has been eminently suc- 

 cessful in experiments on the direct calorimetry of infants, experience 

 with such researches in the Nutrition Laboratory has led us to believe 

 that a type of calorimeter with less mass, less heat capacity, and prob- 

 ably not of the continuous-flow type could most advantageously be em- 

 ployed for the short periods necessitated by experiments with infants. 

 Several types or modifications of calorimeters have been in process of 

 testing for some time, and pending the satisfactory development, con- 

 struction, and testing of an infant calorimeter with the qualifications 

 referred to, we have actively undertaken the study of infant metabolism 

 as determined by indirect calorimetry. In these observations we have 

 devoted our energies to the accurate measurement, in relatively short 

 periods, of the carbon dioxide produced and oxygen consumed by 

 infants less than one year of age. 



There is at present in America a strong movement toward the develop- 

 ment of hospital clinics liberally endowed for scientific research and it is 

 fair to assume that in the next decade the study of infant metabolism 

 will be more actively prosecuted in this country than ever before. 

 Clinicians with whom we have conferred have especially requested 

 that in publishing the results of our observations we should discuss 

 the gaseous metabolism of infants somewhat in detail. Accordingly 

 at this point it seems desirable to define a few of the principles under- 

 lying the method of study. This is done, first, to make clear the 

 methods and technique used in our investigation; and, second, to serve 

 as a guide for those clinicians or experimenters who are interested in 

 actively following this line of research. 



THE RESPIRATORY QUOTIENT AND ITS SIGNIFICANCE. 



The oxygenation of the blood — which, prior to the birth of an infant, 

 was effected by the lungs of the mother — is after birth at once begun 

 through the lungs of the infant. The oxygen is carried by the blood 

 to the various tissues and there enters into the katabolic processes, 

 oxidizing the protein, fat, and carbohydrates. The resulting carbon 

 dioxide is carried by the blood to the lungs and thence excreted into 

 the air which passes though the lungs in respiration, while the partially 

 oxidized nitrogenous products resulting from protein disintegration are 

 excreted through the kidneys. With normal life both the carbohy- 

 drates and fat of the body-material are converted into carbon dioxide 

 and water; protein, also, is in large part changed to carbon dioxide and 

 water, the nitrogenous portion being excreted in the urine in the form 

 of urea, uric acid, and allied compounds. 



The chemical composition of the chief constituents of the body has 

 been determined by analysis and is given in table 12. These values 



