572 



METABOLISM 



amount of energy as when it is slowly oxidized in the animal body. But 

 the case is different for proteins, because these yield less completely oxi- 

 dized end products in the animal body than they yield when burned in 

 oxygen ; so that, to ascertain the physiological energy value of protein, we 

 must deduct from its physical heat value the physical heat value of the 

 incompletely oxidized end products of its metabolism. It is obvious that 

 we can compute the total available energy of our diet by multiplying the 

 quantity of each foodstuff by its calorie value. 



Methods. In order to measure the energy that is actually liberated in the animal 

 body, we must also use a calorimeter, but of somewhat different construction from 



Fig. 174. Respiration calorimeter of the Russell Sage Institute of Pathology, Bellevue Hospital, 

 New York. At the right is seen the table with the absorption tubes; and in the middle, at the 

 back, the electric control table for regulating the temperature of the double walls of the calorimeter. 

 At the extreme left is the oxygen cylinder. (L/usk's Science of Nutrition.) 



that used by the chemist, for we have to provide for long-continued observations and 

 for an uninterrupted supply of oxygen to the animal. Animal calorimeters are also 

 usually provided with means for the measurement of the amounts of carbon dioxide 

 (and water) discharged and of oxygen absorbed by the animal during the observation. 

 Such respiration calorimeters have been made for all sorts of animals, the most perfect 

 for use on man having been constructed in America (see Fig. 174). As illustrating the 

 extreme accuracy of even the largest of these, it is interesting to note that the actual 

 heat given out when a definite amount of alcohol or ether is burned in one of them 

 exactly corresponds to the amount as measured by the smaller bomb-calorimeter. All 



