RESPIRATION. 539 



the rate remain constant and the depth be increased, similar results are 

 obtained. 



The quantity of CO 2 eliminated during slow, deep respirations is larger 

 than during rapid, shallow respirations. 



The diurnal variations are in accord with the changes in the respiratory 

 ra te rising after we awake, falling during the forenoon, again rising after the 

 mid-day meal, again falling during the afternoon, increasing after the evening 

 meal, and falling to a minimum during the night. 



Sunlight exercises a marked influence, as is proven by the results obtained 

 by a number of investigators. In frogs the elimination of CO 2 is increased 

 by sunlight, even after excision of the lungs. Fubini and Benedicenti, 1 in 

 experiments upon hybernating animals, found that the comparative quantities 

 of CO 2 eliminated under the influence of sunlight and of darkness were as 

 100 : 93.48. Confirmatory results have been obtained by Ewald on curarized 

 frogs. 



Eespiratory activity is affected by the character and quantity of the food. 

 The following results, obtained by Pettenkofer and Voit, are very instructive : 



Non-nitrogenous Nitrogenous 

 Fasting. Mixed Diet. Diet Diet 



O 743 grams. 867 grams. 808 grams. 1083 grams. 



C0 2 695 " 930 " 839 " 850 " 



It will be observed that respiratory activity is lowest during fasting, higher 

 when the diet is non -nitrogenous, still higher when the diet is mixed, and 

 highest when the diet is purely nitrogenous. The respiratory quotient is 

 higher when the diet is rich in carbohydrates (p. 545), while it falls in propor- 

 tion to the percentage of nitrogenous food. Fasting reduces the quotient con- 

 siderably, and if coupled with inactivity (hybernation) causes it to fall to a 

 minimum. 



During digestion the gaseous exchange is increased, according to Loewy, 2 

 from 7 to 30 per cent. Joylet, Bergonie, and Sigalas 3 obtained the following 

 averages of seven experiments on a man weighing 52 kilograms, the increase 

 of O being about 7 per cent., and of CO 2 about 6 per cent. : 



CO 2 



o. co 2 . -Q-- 



Before food 259 grams. 298.4 grams. 0.869 



After food 275 " 317 " 0.867 



The increase of respiratory activity during digestion may be due to the 

 chemical processes involved in the production of the digestive secretions, to 

 the oxidation of the products of digestion after absorption, or to muscular 

 activity of the gastro-intestinal walls. Zuntz and Mering 4 endeavored to 



1 Moleschotts Untersuch. z. Naturl, 1887, vol. 14, pp. 623-629. 



2 PftilgeSs Archivf. Physiologic, 1888, vol. 43, pp. 515-532. 



3 Compt. rend., 1887, vol. 105, pp. 380, 675. 



4 Pflugtfs Archiv f. Physiologic, 1883, vol. 32, pp. 173-221. 



