The Living Machine 285 



energy expended in muscular activity. To illustrate the 

 extreme care taken to avoid error in the use of this apparatus 

 may be cited the precautions used in measuring the amount 

 of heat generated by the subject in the calorimeter. This is 

 determined by reading the temperatures of a stream of water 

 which circulates through coils of pipe in the chamber. To 

 the ordinary person it would seem as though it were suffi- 

 ciently accurate to read these temperatures as given by 

 accurate thermometers. But in order to eliminate all possible 

 error corrections are made for the effect of pressure of water 

 on the bulb of the thermometer. "Within the chamber is a 

 folding cot, chair, table and other conveniences. During an 

 experiment the entrance to the chamber is tightly sealed by 

 glass which serves as a window, while a small opening serves 

 for exchange of food, water, excreta, etc. A telephone en- 

 ables the occupant to talk to persons on the outside. The 

 apparatus is so delicate that the slight rise in temperature 

 caused by the subject rising from his chair is recorded by it. 



The respiration calorimeter is used for investigating the 

 many intricate problems of human nutrition and especially 

 for determining the relation between different kinds of food 

 and the energy furnished by them. To test its accuracy its 

 designers performed a series of check experiments in which 

 alcohol instead of human tissue was burned, and the amounts 

 of carbon dioxide, water and heat produced, and oxygen con- 

 sumed, were measured and compared with the amount re- 

 quired by calculation from the amount of alcohol used. Four 

 such experiments showed an average difference between the 

 calculated and experimental results of less than one-half of 

 one per cent. 



Experiments with the calorimeter can be made to show what 

 proportion of the energy available in the food consumed is 

 used in the work done by the subject. It is a fact well known 

 to all mechanical engineers that no machine can utilize all 

 the energy of its fuel. This is largely due to loss of heat by 

 radiation from the surface of the machine and in friction. 

 Our best engines can use perhaps not more than one-tenth 

 of the energy available in their fuel. In this respect the 

 human machine is a more perfect mechanism, for it can use 

 about 15-20% of the energy available in its fuel (food) for 

 mechanical (muscular, nervous, etc.) work. 



The subject of human nutrition is one to fill volumes in 

 itself. We can only note here in passing a few of the most 

 interesting and important results obtained from experiments 

 in this field. 



Two of the perquisites which the Englishman of past 

 generations has regarded as his inalienable right have been 



