382 STUDIES IN ADVANCED PHYSIOLOGY. 



ured, and as the temperature may be equally accurately 

 measured by thermometers, it is no specially difficult task to 

 determine quantitatively the amount of heat under investiga- 

 tion. It is only necessary to take every precaution possible 

 that none of the heat shall be lost by radiation or convection, 

 but that all of it shall be transferred to a known quantity of 

 water and so measured. 



Such calori-metric measurements have been made for a 

 number of substances and the quantity of heat which they 

 produce in burning accurately determined. Thus, one gram 

 of carbon produces 8,080 calories; one gram of hydrogen, 

 34,460; one gram of proteids, 5,778; one gram of fat, 

 9,372, and one gram of sugar, 4,116 calories. One is at 

 first astonished at this stupendous amount of heat. On the 

 other hand, it explains easily how it is possible for a body 

 to derive all its energy and heat from comparatively small 

 amounts of proteids, fats and sugars. 



To the older investigators it seemed impossible that the 

 muscular energy and the large amount of heat lost from a 

 living body should all be derived from the quantitatively 

 small amount of food taken. This error was, however, due 

 to their ignorance of the exact amount of heat which even 

 such small portions of food produce when burned. That 

 this amount of heat seems large is due to the fact that in 

 the every day oxidations of the physical world such a very 

 large proportion of the heat is entirely lost. 



THE AMOUNT OF HEAT LOST BY THE BODY. 



Experiments have been made to determine the amount 

 of heat lost by the human body in a day. These were made 

 by placing the person to be examined in a close-jacketed 

 calorimeter so that all the heat which his body produced 

 could be measured by measuring the temperature of the 

 calorimeter and its water jacket. The experiment was, 

 practically speaking, to confine an individual in a relatively 

 small chamber, or still better, chest, out of which little if 

 any heat could be lost by convection or radiation. The re- 



