RESPIRATION. 375 



Respiratory Activity. The activity or the intensity of the 

 respiratory process may be measured either by the oxygen absorbed 

 or 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 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 functional 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 tissues 

 in twenty-four hours, as shown in the following table: 



QUANTITY OF O AND CO 2 ABSORBED AND EXHALED DURING 

 TWENTY-FOUR HOURS, IN CUBIC CENTIMETERS. 



By 100 Grams of: Oxygen Absorbed. Carbonic Acid Exhaled. 



Muscle, 50.8 c.c. 56.8 c.c. 



Brain, 45.8 " 42.8 " 



Kidneys, 37.0 " 15.6 " 



Spleen, 27.3 " 15.4 " 



Testicles, 18.3 " 27.5 " 



Pounded bones, 17.2 " 8.1 " 



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 conditioned 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 dis- 

 charged. Pettenkofer and Voit found that a man in repose who 

 absorbed daily 807.8 grams of oxygen and discharged 930 grams 

 CO 2 absorbed during work 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. respec- 

 tively. 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 inges- 

 tion of food, materially influences the absorption of oxygen and 



