MEMOIRS Ol- THE NATIONAL ACADEMY OK SCIENCES. 237 



The chamber of the apparatus is so arranged that a man may spend a number of days in 

 comparative comfort within it. It is lighted by a window, and is furnished with a folding chair, 

 table, and lied. and. when the experiment involves muscular work, with a stationary bicycle also. 

 Tin' chamber is ventilated by a measured current of air. samples of which are taken for analysis 

 before it enters and after it leaves the chamber. In this way the products of respiration are 

 determined. Provision is also made for weighing, sampling, and analyzing all the food and drink, 

 and the solid and liquid excreta as well. By comparing the chemical elements and compounds 

 received by the body in food, drink, and inhaled air with those given off in the solid, liquid, and 

 gaseous forms by the intestines, kidneys, lungs, and skin, it is possible to strike a balance between 

 the total income and the total outgo of matter in the man's body. This serves as the measure 

 of the metabolism of matter in the body. 



In addition to this the metabolism of energy is also studied. To this end it is necessary to 

 determine the potential energy of the food and drink taken into the body and of the solid and liquid 

 excreta given off by the body, as well as the amounts of energy given off in the form of heat, 

 externa] muscular work, and otherwise. The measurements of the potential energy of the food 

 ami excreta are made with the bomb calorimeter." The determination of the heat given off from 

 the body is made by certain arrangements in connection with the respiration calorimeter. A 

 current of water passing through a special coil of pipes suspended in the chamber absorbs the 

 heat that is generated within it. and by measuring the quantity of water that passes through the 

 coil and its rise in temperature the amount of heat absorbed may be determined. To this is 

 added the latent heat of the water vaporized within the chamber. 



So delicate are the measurements of temperature that the observer sitting outside and 

 recording the changes every two or four minutes immediately detects a rise or fall of even one 

 one-hundredth of a degree in the temperature of the inner copper wall or of the air inside the 

 chamber. If the man inside rises to move about, the increase in the heat given off from his body 

 with this muscular work shows itself in a rise of temperature which is immediately detected. 



In the work experiments the subject spends a certain portion of each day in muscular 

 exercise upon an apparatus arranged as an ergometer, by which the amount of muscular work done 

 may be measured. The ergometer consists of a stationary bicycle connected with a dynamo by 

 which the power which the rider applies to the pedals, and which is not changed to heat by the 

 friction of the machine, is converted into an electric current, which is passed through an electric 

 lamp and is in turn changed to heat. The ergometer is arranged to measure the amount of 

 muscular work done, in terms of heat, by determinations of the amount of energy converted into 

 heat by friction and the amounts of electric current generated and changed to heat. 



From the energy of food, drink, solid and liquid excretory products, and body material 

 stored or lost the net income of energy may be computed. The net outgo is measured by the 

 apparatus. By comparing these the balance of income and outgo of energy is found. 



The data obtained as explained above, taken in connection with what is known of the 

 physiological processes that go on in the body, give, more accurate information than can be 

 otherwise obtained regarding the ways in which the food is used in the body and the quantities 

 of food ingredients that are needed to supply the demands of the body for the various purposes 

 of work and rest and the comparative nutritive value of different food materials. 



ACCURACY OF APPARATUS AND METHODS. 



Two methods of testing the accuracy of the apparatus are employed. By one method known 

 amounts of heat are generated electrically within the chamber, and the heat is measured by the 

 apparatus. In this way it- accuracy a- a calorimeter only is tested. By the second method 

 known amounts of ethyl alcohol of known purity and composition are burned completely within 

 the chamber, and the amounts of water, carbon dioxide, and heat resulting from the combustion 

 of alcohol are determined by the apparatus. In this way its accuracy both as a respiration appa- 

 ratus and as a calorimeter is tested. In the average of five electrical tests the amount of heat 



* For description of the bomb calorimeter see I'. S. Dept. A.gr., Office Expt, Stations, Bui. 21, pp. 120-126, and 



StuiTs Conn. Experiment Station Report, 1897, p. 199. 



