Discussion of Kesults. 103 



It is therefore highly important that further investigations with the respiration 

 calorimeter be made on individuals of different body-weight, sex, age, etc., to 

 supplement the measurement of the carbon-dioxide production by the still 

 more important measurement of the factors, oxygen consumption and heat 

 production. 



A comparison of the researches thus far made by the two methods is of 

 unusual interest. The research of Sonden and Tigerstedt, undertaken primarily 

 on the grounds of hygiene in connection with school ventilation, is one of the 

 most important contributions to our knowledge of the carbon-dioxide excretion 

 that has ever been made. Unquestionably the results of the Scandinavian 

 investigators can be considered as normal for the conditions obtaining in their 

 experiments. The experiments were sufficiently extended in nature, and a 

 large enough number of individuals was employed to render it highly probable 

 that the results indicate a true average. Our experiments were therefore not 

 made with any idea of repeating or verifying the observations of the Scandi- 

 navian investigators on carbon-dioxide production, but were carried out in 

 connection with a study of the total metabolism of individuals. The carbon- 

 dioxide values are of unusual interest, not only for comparison with the 

 measurements of the other factors, but likewise for comparison with and con- 

 firmation of the results obtained by Sonden and Tigerstedt. 



It is obvious that in experiments on man, to secure results nearest normal, 

 the conditions should approximate the ordinary daily activity and daily bodily 

 conditions; hence, however valuable the researches with special nosepieces or 

 mouthpieces may be for comparison and for other purposes, as a basis for 

 deducing the normal metabolism of man, they can not have the value of those 

 made in connection with experiments where the respiration is free. Conse- 

 quently, in a study of normal metabolism the experiments in this laboratory 

 must of necessity be compared with those made by Sonden and Tigerstedt, since 

 in both sets of experiments the respiration was free and untrammelled. 



Basis of comparison for experiments with special appliances. It is also im- 

 portant to compare the results obtained by the respiration-chamber method 

 with those obtained by the various writers using mouthpieces and nosepieces. 

 Beginning with the early experiments of Smith * and concluding with the 

 more recent researches of Zuntz, we have a long series of most interesting 

 results, which throw light upon the carbon-dioxide production and the oxygen 

 consumption of men lying quietly breathing through special mouthpieces and 

 nosepieces as compared with men sitting in an upright position and breathing 

 normally the air of a special room or chamber. Such comparisons must have 

 value in determining the differences, if any, between the two forms of experi- 

 menting, and for this purpose similarity of body-position is therefore desirable. 

 Unfortunately, by far the larger number of experiments made with the respira- 



1 Smith, Philosophical Transactions, 1859, 149, p. 681. 

 8 



