THE THYROID GLAND AND ITS DISEASES 485 



is meant the minimal heat production of that organism, measured from 

 twelve to eighteen hours after the ingestion of food and with the organism 

 at complete muscular rest. This minimal heat production may be de- 

 termined by direct calorimetry, that is by actual measurement by means 

 of a calorimeter, or by indirect calorimetry, that is by calculating the 

 heat production from an analysis of the end products which result from 

 oxidation within the organism ; in other words, from the amount of oxygen 

 used and the corresponding amount of carbon dioxid produced, together 

 with the total nitrogen eliminated in the urine, although for clinical work 

 the urinary nitrogen may be neglected (Sandiford). 



The experimental work of Lavoisier marks the beginning of researches 

 on metabolism, and to him belongs the credit of pointing out that the 

 life processes are those of oxidation with the elimination of heat. 



In 1894 Kubner (b) constructed the first successful respiration calorim- 

 eter designed for the measurement of the gaseous exchange between a 

 living organism and the atmosphere which surrounds it and the simulta- 

 neous measurement of the quantity of heat produced by that organism. 

 By means of this apparatus Rubner (6) verified the method of Pettenkoffer 

 and Voit of calculating the heat production (indirect calorimetry) and 

 proved that the law of conservation of energy holds for the living organism. 



It was not until 1905 that the respiration calorimeter was brought 

 to a high degree of technical perfection by Atwater and Benedict, With 

 their apparatus it was possible to determine simultaneously with the 

 measurement of the heat elimination, not only the carbon dioxid pro- 

 duction, but also the oxygen consumption of the subject. They also con- 

 firmed the agreement between direct and indirect calorimetry. Lusk, 

 Du Bois, Peabody, and their coworkers have likewise demonstrated, in a 

 large series of pathologic conditions, the close agreement between the two 

 methods. As a result of these investigations the use of such a complicated 

 apparatus as the respiration calorimeter has been shown to be unnecessary 

 for clinical work and in its place the comparatively simple method of 

 indirect calorimetry to be adequate. 



Carpenter has shown that for indirect determination two types of ap- 

 paratus are suitable, the closed circuit and the gasometer. According to 

 Sandiford, by far the best apparatus of the closed circuit type is the Bene- 

 dict (a) unit apparatus. By means of a mask, mouthpiece or nasal tubes, 

 the subject rebreathes air from a closed system in which the carbon 

 dioxid is absorbed by soda lime, and, as the oxygen is used up, it is 

 replaced by oxygen in known amounts. The air within the apparatus 

 is kept in constant circulation by means of a blower. A small spirometer 

 is inserted in the circuit as an expansion chamber and volumetrically 

 records the respiratory movements on a smoked drum. Knowing the 

 weights of oxygen used and the carbon dioxid eliminated, one can readily 



