RESPIRATION 427 



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 hand. 



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, the former is usually taken as the index of the activity, though 

 there are reasons for believing that it would be more accurately indicated or 

 represented 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- 

 tional activities, being least in bones and greatest in muscles. This is shown 

 by the relative amounts of oxygen absorbed and carbon dioxid discharged 

 by equal amounts of each of these and other living tissues in twenty-four 

 hours, as given in the following table : 



QUANTITY OF O 2 AND CO 2 ABSORBED AND EXHALED DURING TWENTY-FOUR 

 HOURS, IN CUBIC CENTIMETERS 



Oxygen Carbon Dioxid 



By 100 Grams of: Absorbed. Exhaled. 



Muscle... 50.8 c.c. 56.80.0. 



Brain 45. 8 c.c. 42. 8 c.c. 



Kidneys 37 -o c - c - *5 -6 c.c. 



Spleen 27 .3 c.c. 15 .4 c.c. 



Testicles 18.30.0. 27.50.0. 



Pounded bones 17 .2 c.c. 8.1 c.c. 



The total respiratory change therefore of the body as a whole is the resultant 

 of the respiratory changes of its individual organs and tissues, and is condi- 

 tioned by all influences which retard or hasten their activity. Among 

 these influences the more important are the following: 



Muscle Activity. As the muscles constitute a large part of the body, 

 about 40 per cent., and as muscle- tissue absorbs and discharges relatively 

 large quantities of oxygen and carbon dioxid, it is readily apparent that an 

 increase in their activity would be followed or attended by an increase in the 

 respiratory exchange. In passing from a condition of body repose to one of 

 marked activity there ought to be an increase in the amount of oxygen 

 absorbed and CO 2 discharged. Pettenkofer and Voit found that a man in 

 repose who absorbed daily 807.8 grams of oxygen and discharged 930 

 grams CO 2 , absorbed duringwork 1006 grams of oxygen and discharged 1137 

 grams of CO 2 . Edward Smith, who estimated only the CO 2 , found that a 

 man in repose who discharged carbon dioxid at the rate of 161.6 c.c. per 

 minute increased the amount while walking at the rate of two and three 

 miles an hour to 569 c.c. and 851 c.c. respectively. Similar results have been 

 obtained by other investigators. 



Digestive Activity. The activity of the alimentary canal, involving 

 contraction of its muscle coat through its entire length as well as secretion 

 of its related glands called forth by the ingestion of food, materially influences 

 the absorption of oxygen and discharge of carbon dioxid, independent of the 



