538 METABOLISM 



of pipe in the chamber. The heat used to vaporize the moisture from 

 skin and lungs must of course also be measured. This is done by collect- 

 ing the water vapor in a sulphuric-acid bottle placed in the ventilat- 

 ing current. By multiplying the grams of water by the factor for the 

 latent heat of vaporization, we obtain the calories of heat so eliminated. 



' * The calorimeter contains a comfortable bed and is provided with two 

 windows, a shelf, a telephone, a fan, a light, and a Bowles stethoscope for 

 counting the pulse. The ordinary experiment takes about as long as a trip 

 from New York to New London. Patients, as a rule, doze from time to 

 time or else try to work out some scheme by which they can amuse them- 

 selves without moving. After three or four hours they are rather bored 

 by the quiet, and the observations are not prolonged beyond this time. 

 They are allowed to turn over in bed once or twice an hour, but reading 

 and telephoning are discouraged, since these increase the metabolism. 

 The air in the box is fresh and pure, the patient suffers no discomfort, and 

 objections to the procedure are very infrequent. Most of the patients 

 are only too glad of the extra attention, and they insist that the calor- 

 imeter has a marked therapeutic value." (Du Bois.) 



Normal Values. — Having thus satisfied ourselves as to the extreme 

 accuracy of the method for measuring energy output, we shall now con- 

 sider some of the conditions that control it. To study these we must first 

 of all determine the basal lieai production — that is, the smallest energy 

 output that is compatible with health. This is ascertained by allowing a 

 man to sleep in the calorimeter and then measuring his calorie output 

 while he is still resting in bed in the morning, fifteen hours after the last 

 meal. When the results thus obtained on a number of individuals are 

 calculated so as to represent the calorie output per kilogram of body weight- 

 in each case, it will be found that 1 C. per kilo per hour is discharged 

 —that is to say, the total energy expenditure in 24 hours in a man of 70 

 kilos, which is a good average weight, will be 70X24 = 1,680 C. 



When food is taken the heat production rises, the increase over the 

 basal heat production amounting for an ordinary diet to about 10 per 

 cent. Besides being the ultimate source of all the body heat, food is there- 

 fore a direct stimulant of heat production. This specific dynamic action, 

 as it is called, is not, however, the same for all groups of foodstuffs, being 

 greatest for proteins and least for carbohydrates. Thus, if a starving 

 animal kept at 33° ( !. is given protein with a calorie value which is equal 

 to the calorie output during starvation, the calorie output will increase by 

 :;i) per cent, whereas with carbohydrates it will increase by only G per 

 cent. Evidently, then, protein liberates much free heat during its as- 

 similation in the animal body; it burns with a hotter flame than fats or 

 carbohydrates, although before it is completely burned it may not yield 



