Water of Kespiration. 435 



44.3 grams, and for the same period on the first day in experiment No. 76 it 

 was 50.1 grams. A similar comparison holds for practically all the periods 

 of the experiment, so that there is a slight positive increase in the elimination 

 of water-vapor accompanying the ingestion of these small amounts of food. 

 This may well be ascribed to the slight additional internal muscular activity 

 called for on the ingestion of food. 109 A portion of the increase may also result 

 from the rise in the respiration rate and the increased muscular activity as a 

 whole indicated by the change in pulse rate. 



Proportions of water-vapor eliminated from the lungs and shin. The two 

 chief opportunities for the vaporization of water are from the lungs and from 

 the skin. Air taken into the lungs containing a varying amount of water- 

 vapor is expelled saturated with water-vapor at the temperature of the body. 

 The volume of air thus taken into the lungs and its relative humidity thus 

 determines the total amount of water-vapor leaving the body in the expired 

 air. The evaporation of water from the skin is not so directly measurable, 

 since the quantity thus vaporized may show wide variations. The air in con- 

 tact with the skin is certainly not saturated with water-vapor at the external 

 temperature of the body. Furthermore, the clothing and the interlying air- 

 spaces produce, so to speak, an artificial atmospheric environment. These 

 air-spaces may contain widely varying amounts of water-vapor according to 

 the thickness of the layer of air, the movements of the subject and the tempera- 

 ture of the air as well as the external temperature of the body. Many attempts 

 have been made to measure directly the water-vapor expelled from the lungs. 

 Such measurements, save for experiments of short duration, are impracticable. 



The data obtained in the Middletown experiments give the total water of 

 respiration and perspiration for each 2-hour period and for the day. By an 

 indirect method of calculation, it is possible to apportion these amounts in 

 such a manner as to estimate the amount exhaled from the lungs and thus 

 show how the vaporization of water is divided between the lungs and skin. 

 With this form of respiration apparatus, no direct measure of the actual venti- 

 lation of the lungs is at hand. Since, however, the amount of oxygen absorbed 

 is accurately determined, it is possible to form a reasonably accurate estimate 

 of the total ventilation of the lungs from the knowledge of the oxygen con- 

 sumption. Zuntz uo and his associates have found in a brilliant series of 

 experiments that for every cubic centimeter of oxygen consumed by a man at 

 rest, 21 cc. of air are inspired. Using this ratio, therefore, it is possible to 

 compute the total ventilation of the lungs by multiplying the total oxygen 

 consumption by 21. 



109 The marked difference in muscular activity in experiments Nos. 69 and 70 

 explains the one exception to the above comparisons. 



u0 H6henklima und Bergwanderungen in ihrer Wirkung auf den Menschen, N. 

 Zuntz, A. Loewy, Franz Muller, W. Caspari (1906), Berlin, p. 380. 



