NORMAL PEOCESSES OF ENERGY METABOLISM 573- 



The increase in temperature is observed by continuous readings of ther- 

 mometers placed in the inlet and other thermometers placed in the cur- 

 rent after it has passed over the man's body. The heat elimination is found 

 by multiplying the volume of air by factors converting it to weight, by its 

 specific heat and by the average rise in temperature. 



The two methods of Lefevre just described are well suited for a study 

 of the influence of environing temperature upon heat production. One has 

 only to vary the temperature of the bath or current of air before it strikes 

 the body to vary the cooling effect. Lefevre combined the water-bath meth- 

 od with a method for obtaining the respiratory exchange. 



2. The Atwater-Rosa-Benedict Respiration Calorimeter (Atwater and 

 Benedict )(d). The fundamental principles of this apparatus which was 

 designed to measure accurately the heat elimination of a man, are as fol- 

 lows : The subject is confined in a heat-proof chamber through which a cur- 

 rent of ^ cold water is kept constantly passing. The amount of water, the 

 flow of which is kept constant, is carefully weighed. The temperatures of 

 the water entering and leaving the chamber are read at frequent intervals 

 on sensitive thermometers to 0.01 of a degree. The walls of the chamber 

 are held at such a temperature as to prevent the loss of any heat through 

 them, and withdrawal of heat by the water current is so regulated by vary- 

 ing the temperature of the ingoing water that the heat brought away from 

 the calorimeter is exactly equal in amount to the heat eliminated by radia- 

 tion and conduction from the subject. This is accomplished by having ac- 

 curate knowledge of the temperature of the air inside the apparatus and 

 the temperature of the walls of the calorimeter. About 25 per cent of the 

 heat produced by the human subject is eliminated at ordinary temperatures 

 through vaporization of water from the lungs and the skin. This latent 

 heat in the water of vaporization is determined by measuring the amount 

 of water vaporized and passing in the ventilating current to the first sul- 

 phuric acid absorber. The gain in. weight of this absorber is taken as the 

 water of vaporization. 



The respiration chamber of this calorimeter has been constructed in 

 several different sizes. The original construction at Middletown, Conn., 

 had a chamber with a cubic capacity of 5.03 cubic meters, or with the sub- 

 ject inside a residual air volume of 4500 liters. This apparatus was dis- 

 mantled at the time the Nutrition Laboratory of the Carnegie Institution 

 was established at Boston and in its place have been constructed a number 

 of different calorimeters (Benedict and Carpenter (a)) designed for dif- 

 ferent purposes. The first of these known as the chair calorimeter (Fig. 

 25) has a cubic capacity of approximately 1400 liters. A .second con- 

 struction known as the bed calorimeter (Fig. 36) has a cubic capacity of 

 1347 liters. That part of the original Atwater-Rosa calorimeter which 

 was the property of the U. S. Government was shipped to Washington and 

 has been reconstructed into a successful calorimeter by Langworthy and 



