Carbon-Dioxide Elimination. 149 



The majority of experiments on the quantitative relations of the amounts of 

 water vaporized from the lungs and skin of man have been made either for the 

 purpose of studying general problems of hygiene (like those of Sonden, Tiger- 

 stedt and Eubner), problems which could well be solved by researches with 

 only an approximate degree of accuracy, or the water determinations were made 

 for the evidence they presented as to the energy required to vaporize the water 

 (as in the experiments made by Atwater and his associates). It is clear from 

 the foregoing consideration that researches are needed for the study of the 

 water-vapor elimination per se. Such researches should be taken into consid- 

 eration, the respiration from the lungs and skin each studied separately, and 

 the many factors influencing such transpiration, as body-temperature, espe- 

 cially during pyrexia, muscular activity, clothing, movement of the air, external 

 temperature, and variations in the rate of circulation of the blood. 



Carbon-Dioxide Elimination, 

 earlier investigations. 



The close relationship between the combustion of fuel and the production of 

 carbon dioxide on the one hand, and vital activity and the exhalation of carbon 

 dioxide on the other, early led to a careful study of this product of respiration. 

 Fortunately, the determination of the proportion of carbon dioxide in the ex- 

 pired air presents no special difficulty, since the methods for determining 

 carbon dioxide, either volumetric or gravimetric, are exceedingly accurate. It 

 is somewhat difficult, however, to determine quantitatively the carbon dioxide 

 exhaled from the human body in the course of an experimental period, as this 

 usually involves a knowledge of the volume of the total air expired, and the 

 methods for measuring the total air expired during an experimental period 

 have not been perfected and are still open to criticism. 



The earlier attempts to determine the total 24-hour output of carbon dioxide 

 have been discussed in detail by other writers, 1 and it is unnecessary here to 

 go into a lengthy historical account of the methods employed. Many of the 

 earlier results are of general interest when viewed in the light of results ob- 

 tained by modern methods, and hence it is fitting that such of the earlier work 

 as possesses a distinct physiological as distinguished from an historical interest 

 should here be reviewed. 



The early observations of Lavoisier and Seguin have an unusual interest, 

 since the estimation of the oxygen required by resting man as made by them co- 

 incides with wonderful accuracy with determinations made by the best methods 

 of the present day. The carbon-dioxide determinations reported by these in- 

 vestigators, however, fluctuate widely. In the memoir 2 of 1789 they state that 



1 Zuntz, Hermann's Handbuch der Physiologie, 1S82, 4, 44, p. 118. 



2 Lavoisier and Seguin, Premier Memoire sur la Respiration des Animaux. His- 

 toire de l'Academie des Sciences, Paris, 1789, pp. 566-584. 



