Carbon-Dioxide Elimination. 161 



as years progressed, the technique rapidly improved until finally at the present 

 time we have a number of excellent methods for determining the carbon- 

 dioxide production; (2) the influence of a number of factors on respiratory ex- 

 change is distinctly shown and consequently, to make experiments strictly com- 

 parable, it is necessary that the experiments be made at given hours of the day 

 and with due regard to diet, muscular activity, and the size of the subject. 



The earlier experiments were almost invariably made with the express pur- 

 pose of studying the respiratory exchange as affected by some particular factor. 

 Aside from the experiments of Sonden and Tigerstedt, 1 and Magnus-Levy and 

 Falk, 2 few researches have been made on the normal carbon-dioxide output 

 of resting man, and hence the results here collected represent the largest num- 

 ber of experiments on different individuals made by modern methods that has as 

 yet appeared. 



EXPERIMENTS ON CARBON-DIOXIDE ELIMINATION. 



The carbon-dioxide elimination of man during fasting has been discussed 

 at considerable length in a previous publication, 3 and especial stress is laid 

 only upon those among the earlier experiments that are strictly comparable 

 with those here reported. It is obvious that the ingestion of food, and muscular 

 exercise both play an important role in the excretion of carbon dioxide. It is 

 the purpose of this report to discuss in more detail the factors influencing the 

 carbon-dioxide production, and since it was found with the water elimination 

 that the more constant conditions for comparison were obtained during sleep, 

 i. e., when no food was taken and when the muscular activity was relatively 

 constant, the carbon-dioxide production of men during sleeping hours is first 

 considered. Fortunately, a large number of experiments were made in which 

 the carbon-dioxide production during sleep was determined with considerable 

 accuracy. 



Since it is obvious from the earlier literature that the body-weight of the 

 subject plays an important role in the total carbon-dioxide excretion, in pre- 

 senting the material regarding the carbon-dioxide excretion herewith, it has been 

 deemed advisable to give not simply the amount per hour but likewise the 

 amount per kilogram of body-weight per hour and per square meter of body- 

 surface per hour. Many of the earlier writers have computed their results upon 

 the basis of volume of carbon dioxide expired, and consequently our results are 

 also presented on the basis of cubic centimeters per minute, per kilogram of 

 body-weight per minute, and per square meter of body-surface per minute. 



CARBON-DIOXIDE ELIMINATION DURING SLEEP. 



The values given in table 67 are the average values obtained in observations 

 from 1 a. m. to 7 a. m., with different individuals. With one individual 

 only 1 experiment was made, with others as many as 20; but as during the 



1 Sonden and Tigerstedt, loc. cit. 



2 Magnus-Levy and Falk, loc. cit. 



s Benedict, Carnegie Institution of Washington Publication No. 77, 1907. 



