PREVIOUS INVESTIGATIONS. 13 



as that used by Fyfe and Prout. Emphasis was laid solely upon the 

 percentage of carbon dioxide in the expired air. The subject expired 

 into a rubber bag having a capacity of 1,000 cubic inches; samples of 

 air were then taken from this bag, the carbon dioxide being absorbed 

 with lime-water. Experiments were made both before and after food. 

 Coathupe concluded that the carbon dioxide produced in respiration is 

 less during the period of active digestion, that it increases with increased 

 abstinence from food, and that it varies with the same individual at 

 similar periods of different days; excitement of any kind causes a 

 decrease. 



It is obvious that the researches of Jurine, Prout, Fyfe, and Coathupe, 

 dealing as they do only with the percentage of carbon dioxide in the 

 expired air, contribute but little of value to our knowledge of the actual 

 changes in the total metabolism incidental to the ingestion of food. 

 Until 1843, therefore, the only quantitative data on this subject to 

 be found in the literature are those obtained in the research of Lavoisier 

 and Se*guin, in which it was noted that approximately a 50 per cent 

 increase in the oxygen consumption followed the ingestion of food. 



Scharling, 1843. A considerable period of time intervenes between 

 the early experiments of Lavoisier and the next stage of definite evi- 

 dence. For the purpose of making direct determinations of the carbon 

 dioxide produced by man, Scharling 1 constructed a large wooden box 

 having a capacity of approximately 1 cubic meter and ventilated by a 

 pump. The expired air was passed over a chain of glass vessels con- 

 taining sulphuric acid, caustic potash, sulphuric acid, and lime-water 

 respectively. The carbon-dioxide content of the air in the chamber 

 was determined at the beginning and the end of the experiment. The 

 periods were usually 1 hour long, although sometimes varying from 90 

 to 30 minutes; not more than one or two observations were made in 

 24 hours. The subjects, six in number, were allowed to read, talk, sew, 

 write, etc., so complete muscular repose was not observed. The 

 results given for each subject are the carbon-dioxide production in 

 grams for the individual periods and per 24 hours, the pulse rate 

 before and after meals, the ratio between day and night for the carbon- 

 dioxide production, and the ratio between body mass and the carbon- 

 dioxide production. Although the experimental technique has been 

 criticized by Zuntz, 2 who has shown that undoubtedly carbon dioxide 

 escaped absorption, nevertheless the general conclusions obtained 

 by Scharling are not without interest, for he concludes that, other 

 things being equal, man expires more carbon dioxide after he has eaten 

 than when he is without food, and more when he is awake than when he 

 is asleep. He finds that the maximum carbon-dioxide output occurs 



'Scharling, Ann. d. Chem. u. Pharm., 1843, 45, p. 214; reprinted in detail in Ann. d. China. 



et d. Phys., 1843, aer. 3, 8, p. 478. 

 2 Zuntz, Hermann's Handb. d. Physiol., 1882, 4, (2). p. 123. 



