Respiration Calorimeter 201 



energy production. The older forms of respiration ap- 

 paratuses simply allowed an estimation of the carbon 

 dioxid and water given off by the animal. How much 

 of the water was formed by the oxidation of the 

 hydrogen of the food and how much was simply evapo- 

 rated from the store taken in as water, it was impos- 

 sible to know by direct determination. This could 

 only be calculated. The carbon dioxid was, on the 

 other hand, a direct and accurate measure of the com- 

 bustion of carbon. Later devices, as, for instance, the 

 one used by Zuntz, allow a direct determination, not 

 only of the products of combustion, but of the oxygen 

 absorbed by breathing. This method of work has 

 great advantages, as one measurement not only checks 

 the other, but makes it possible to ascertain the actual 

 oxygen consumption during any given period of the 

 experiment, as, for instance, when the animal is at 

 rest, when masticating food, or when performing a 

 given amount of external work. In this way, Zuntz 

 made his masterly demonstrations of the differences 

 in the net values of different foods due to the greater 

 energy cost of masticating and digesting certain ones. 

 Respiration calorimeter. — None of the older appara- 

 tuses, whether allowing the determination of oxygen 

 consumption or not, measured the heat radiation from 

 the animal body, or, in other words, the amount of 

 energy actually evolved from internal combustion. 

 Recently Professors Atwater and Rosa have devised a 

 respiration apparatus which is at the same time a cal- 

 orimeter. The quantity of heat radiated from a man 

 or other animal confined in this calorimeter is absorbed 



