144 Metabolism of Healthy Man. 



490 grams, respectively, during a 12-hour experiment in the night. During 

 the whole experiment the subject was in bed, covered with bed-clothing, and 

 lying quietly and for the most part asleep. The temperature of the chamber 

 varied from 17.4 to 19.1 C. 



RELATIVE AMOUNTS OF WATER VAPORIZED FROM THE LUNGS AND SKIN. 



Method of Computation. 

 The water vaporized from the body of a subject inside the respiration cham- 

 ber is made up in part of water vaporized from the skin, and in part of water 

 taken up by the air inspired into the lungs. It is of interest to secure evidence 

 with regard to the partition of this water between that vaporized from the 

 lungs and that from the skin. Thanks to a method of computation presented 

 by Zuntz, 1 Ave are able to make an approximate estimation of these relative 

 proportions. 



Assuming that the air inspired has the moisture-content of the air in the 

 chamber and that the expired air is saturated " with moisture at the tempera- 

 ture of the body, 37 C, it is possible, if we know the total ventilation of the 

 lungs, to compute the output of water-vapor through the lungs. In our experi- 

 ments the total ventilation of the lungs was not directly determined, as it is 

 in the experiments with the Zuntz apparatus. As a result of a number of 

 experiments with trained subjects with the Zuntz apparatus, Zuntz and his 

 associates found that, for every liter of oxygen absorbed, there was a ventilation 

 of the lungs of 21 liters of air, and hence if we multiply the volume of oxygen 

 absorbed in these experiments by 21, we have an approximate measure of the 

 total ventilation of the lungs. This calculation has been carried out with many 

 of the experiments here reported, and the apportionment of the water-vapor 

 between the lungs and skin has been made upon this basis. Obviously there 

 are many chances for error in a computation of this kind, since the ratio of 

 oxygen absorbed to the total ventilation varies somewhat with different subjects 

 even at rest, but averaging the results of a large number of experiments, such 

 as are here collected, the values are probably fairly representative of the true 

 ventilation conditions. 



It has been found in the majority of our experiments that the respiration- 

 rate varies little from hour to hour, and consequently there will be a reasonably 

 constant elimination of water-vapor through the expired air. Where there are 

 variations in respiration rate, there may be a larger amount of air taken into 

 the lungs and consequently a greater amount of water carried out with the 

 saturated air. It is still to be proved, however, that with an increased respira- 



1 Zuntz, Loewy, Muller, and Caspari, Hohenklima und Bergwanderungen, Berlin, 

 1906, p. 380. 



2 At rest this is probably true. With the forced respiration accompanying mus- 

 cular work, Rubner and Lesage maintain that the expired air is not saturated. (See 

 discussion of this point by Benedict, Carnegie Institution of Washington Publication 

 No. 77, 1907, p. 436.) 



