Fyfe, 1814

At about the same time as Prout's experiments, a number of observations were made by Andrea Fyfe,2 of Edinburgh, which form the basis of a communication made by Prout in 1814.3 Like Prout, Fyfe dealt exclusively with the percentage of carbon dioxide in the expired air. The expired air was collected in a bell-jar holding approximately 2.5 liters; the proportions of carbon dioxide and oxygen were then determined by means of a Hope eudiometer with the use of lime-water and sulphuret of lime. In an extensive series of experiments in which vegetable diets were given, Fyfe reports that the percentage of carbon dioxide fell from 8.5 per cent before the food experiment to about 4.5 per cent on the seventh and eighth days of the test. The experiments with animal diet lasted 8 days; on the fourth day the carbon dioxide was 7 per cent and on the seventh and eighth days 5 per cent. A repetition of the experiment gave values for the carbon-dioxide content on the third, fourth, fifth, sixth, and seventh days of 6 to 7, 7, 9, 5, and 8 per cent, respectively. When wine was taken, the carbon dioxide in the expired air was reduced in one experiment to between 2 and 3 per cent, and in another to 5.75 per cent.

Coathupe, 1839

Twenty-five years after the experiments of Fyfe, Coathupe4 made a series of observations on the products of respiration at different periods of the day, employing much the same apparatus 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.

1Scharling, Ann. d. Chem. u. Pharm., 1843, 45, p. 214. He speaks of Prout's results as being published in the Journ. f. Chem. u. Physik von Schweigger, 1815, 15, p. 65.

2Fyfe, Dissertatio Chemico-Physiologica Inauguralis de Copia Acidi Carbonici e Pulmonibus inter respirandum evoluti, 1814.

3Prout, Annals of Philosophy, 1814, 4, p. 331.

4Coathupe, Phil. Mag., 1839, 3d ser., 14, p. 401.

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 Seguin, 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 evidence. For the purpose of making direct determinations of the carbon dioxide produced by man, Scharling1 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 containing 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 after the main meal of the day, independent of the hour at which it is taken. Scharling did not overlook the importance of noting the pulse rate, both in the fasting experiments and in those preceding and following the ingestion of food. Although his results may now have but little quantitative value, it is of importance to note that Scharling was the first to employ successfully the chamber principle of studying the respiratory exchange.

1Scharling, Ann. d. Chem. u. Pharm., 1843. 45, p. 214; reprinted in detail in Ann. d. Chim.

*et d. Phys., 1843, ser. 3, 8, p. 478. 2Zunti, Hermann's Handb. d. Physiol., 1882, 4, (2). p. 123.