RESPIRATION. 413 



employed is completely closed, the carbon dioxid must be removed as soon 

 as discharged and the oxygen renewed as soon as absorbed. The former is 

 accomplished by the aspiratory action of moving bulbs containing an alkali, 

 the latter by a steadily acting pressure on a reservoir of oxygen. This 

 apparatus consists essentially of a glass bell-jar in which the animal is 

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

 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. 1 



Of the results obtaind 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 grams. Pettenkofer and Voit. 800 grams. 



663 grams. Speck. 770 grams. 



The amounts of oxygen absorbed in Pettenkofer and Voit's experiments 

 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 surplus 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 kilo- 

 gram) and to the unit of time (one hour). 



Respiratory Activity. The activity or the intensity of the respiratory 

 process may be measured either by the oxygen absorbed or by the carbon 

 dioxid discharged. But as the carbon dioxid is more easily estimated than 

 the oxygen, it is usually taken as the index of the activity, though there are 

 reasons for believing that it would be more accurately indicated or repre- 

 sented by the oxygen. 



Whatever factor may be accepted as the measure, it is certain that the 

 respiratory activity varies in different tissues in accordance with their func- 



1 Both forms of apparatus are in use in the Physiological Laboratory of the Jefferson 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. 



