6 Metabolism of Healthy Man. 



with the greatest possible muscular relaxation, and the experiments are for 

 the most part of but a few minutes' duration. For studying specific problems 

 in the chemistry of digestion such experiments are of incalculable value. For 

 throwing light on the normal metabolism of man they have but little value, 

 as these men were abnormally quiet, rarely asleep, and with the greatest en- 

 forced muscular relaxation. No conditions existing in ordinary life approxi- 

 mate this except, perhaps, the time in bed when not asleep. 



Furthermore, the most satisfactory and valuable researches with this type of 

 apparatus have been made on men who were trained subjects. As early as the 

 investigations of Speck, 1 it was clear to him that results were obtained on others 

 only after long painstaking training in breathing through the mouthpiece. 

 Some of Zuntz's associates, more venturesome, have used the apparatus on 

 hospital patients and presumably have considerable confidence in the accuracy 

 and value of the results thus obtained. It is admitted by all, however, that 

 respiration through a mouthpiece is not normal and that the subjects have a 

 considerable sense of restraint. On the other hand, it may be contended by 

 some that the confinement inside the respiration chamber may likewise produce 

 a feeling of restraint. It has been our experience (and this is wholly in accord 

 with the experience of the Scandinavian investigators and of Rubner, and 

 Pettenkofer and Voit) that the time required to accustom a person to life 

 inside the respiration chamber is rarely more than an hour or two. Usually 

 the subjects are comfortably seated, reading, and suffer no discomfort. For 

 the study of the metabolism of normal man it is obvious that any feeling of 

 discomfort, strain, forced muscular relaxation, or other artificial condition, 

 must be minimized. From our extensive experience, both with respiration 

 appliances, and witli the chamber method, we feel confident in saying that the 

 conditions are infinitely more normal with the respiration chamber than with 

 the usual device for mouth or nose breathing. 



In an attempt to render more normal and less painfully annoying the breath- 

 ing through special appliances, an improved form of nosepiece lias been de- 

 veloped in this laboratory 2 that can be worn for considerable periods of time 

 without discomfort and has given results that approach the nearest to normal 

 of any form of breathing appliance with which we are at all familiar. 



With the improved methods for studying metabolism, investigators have 

 made a large number of experiments on normal, healthy men, in an attempt 

 to provide sufficient scientific basis for subsequent studies of men in disease. 

 A knowledge of the respiratory products is of incalculable advantage in deter- 

 mining the nature of the metabolism as well as the total metabolism. Indeed, 

 many investigators have used the carbon-dioxide production and oxygen con- 

 sumption to compute the total metabolism of normal man. 



Of the two methods for studying the total metabolism, and particularly the 

 respiratory exchange, namely, the one in which the subject remains inside of a 



1 Speck, hoc. cit., p. 215. 2 Benedict, Amer. Journ. Physiol., 1909, 24, p. 345. 



