536 



METABOLISM 



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

 the ease is differenl 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 energv that is actually liberated 



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. ( Lusk's Science of Nutrition.") 



in the animal body, we must also use a calorimeter, but of somewhat dif- 

 ferent construction from that used by the chemist, for we have to provide 

 for long-continued observations and for an uninterrupted supply of oxy- 

 gen 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 prefect for use on man having been constructed in America (see Pig. 

 171 . As illustrating the extreme accuracy of even the largest of these, 



