RESPIRATION 423 



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 m the following table: 



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 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. 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 

 increase due to the oxidation of food materials after absorption. It was 

 found that in a fasting man a dose of sodium sulphate increased the absorp- 

 tion of oxygen as much as 17 per cent, and the discharge of CO 2 24 per cent. 

 (Lowy). It is difficult to determine how much of the increase after a meal 

 is therefore due to food oxidation and how much to functional activity 

 of the canal itself. The consumption of nitrogenized meals, however, has 

 a greater effect than non-nitrogenized meals. 



Temperature. A rise in temperature of the surrounding air has as 

 an effect diminution in the amounts of oxygen consumed and carbon 

 dioxid discharged. A fall in temperature has the opposite effect. Thus 

 a cat at a temperature of 3-2C. consumed during a period of six hours 

 21.39 grams of oxygen and discharged 22 grams of carbon dioxid, while at 

 a temperature of 29.6C. the corresponding amounts for the same period < 

 time were for oxygen 13.9 grams and for carbon dioxid 13.12 grams. Lavoi- 

 sier and Sequin, having reference only to the oxygen, found that a man 



