3 74 TEXT-BOOK OF PHYSIOLOGY. 



dioxid must be removed as soon as discharged and the oxygen re- 

 newed as soon as absorbed. The former is accomplished by the as- 

 piratory action of moving bulbs containing an alkali, the latter by a 

 steadily acting pressure on a reservoir of oxygen. This apparatus 

 (Fig. 179) consists essentially of a bell-jar in which the animal is 

 placed. This is brought into connection by tubes, on the one 

 hand, wiith the oxygen reservoir, and, on the other hand, with the 

 aspiratory bulbs, kept in motion by some form of motor. The 

 construction of each of these forms of apparatus is so complex, the 

 conduct of an experiment and the final determination of the results 

 so complicated, that a detailed description would be out of place in 

 a work of this character.* 



Among the results obtained by these and other methods a few are 

 given in the following table: 



Oxygen Absorbed. Observer. Carbon Dioxid Discharged. 



746 grams. Vierordt. 876 grams. 



700 " Pettenkofer and Voit.^ 800 



663 " Speck. 770 



The amounts of oxygen absorbed in Pettenkofer and Voit's experi- 

 ments varied from 594 to 1072 grams; of carbon dioxid exhaled, from 

 686 to 1285 grams. 



In all these results it is evident on examination that the volume 

 of oxygen absorbed is always greater than the volume of carbon 

 dioxid exhaled, or, what amounts to the same thing, the weight of the 

 oxygen absorbed is always greater than the weight of the oxygen 

 entering into the formation of the carbon dioxid exhaled. The reason 

 for this difference between the amounts of oxygen in the inspired air 

 and in the CO 2 exhaled is found in the fact that on a mixed diet one 

 containing fat a portion of the oxygen is utilized in the oxidation 

 of the hydrogen of the fat with the formation of water. Under such 

 a diet the respiratory quotient is always less than unity, usually 

 0.907. On a purely carbohydrate diet one in which there is no 

 surplus hydrogen all the oxygen will combine with carbon and be 

 returned as carbon dioxid, and hence the respiratory quotient will 

 be unity. The respiratory quotient therefore indicates the extent to 

 which the oxygen absorbed is utilized in oxidizing carbon, on the one 

 hand, and hydrogen, on the other. 



Since the total oxygen absorbed and carbon dioxid discharged 

 will vary considerably with the size of the animal, it is customary, 

 for purposes of comparison, to reduce all total results to the unit of 

 body- weight (one kilogram) and to the unit of time (one hour). 



* Both forms of apparatus are in use in the Physiological Laboratory of the Jeffer- 

 son Medical College and are fully described by Prof. H. C. Chapman in his text- 

 book on Physiology, to which the reader is directed for further information. 



