TECHNIQUE FOR METABOLISM DURING REST. 87 



chair. When used for experiments with the subject in the standing 

 position, the base is mounted on a wooden box of the desired height. 



BREATHING APPLIANCES. 



For the sake of simpHcity in this description of the portable respira- 

 tion apparatus, and since it was regularly used in all our experiments, 

 the mouthpiece only is referred to and shown in the diagram, but we 

 have reason to believe that the original form of inflated nosepiece used 

 in the Nutrition Laboratory may be of even greater practical value, 

 inasmuch as it has less influence upon the type of respiration.^ 



At first sight the use of a mask in a closed-circuit apparatus of this 

 type would seem impracticable, as the slightest leak between the mask 

 and the face would have a pronounced effect upon the measurement of 

 the oxygen. Actual experience with the mask in the Nutrition Labo- 

 ratory has, however, given good results. This form of breathing appli- 

 ance is much more comfortable for subjects, permitting as it does free 

 nose and mouth breathing, without the objectionable features of the 

 mouthpiece. 



AIR-MOISTENER. 



Since with any type of breathing appliance the purified air passing 

 along the tube is too dry to be breathed comfortably by the subject, a 

 small moistening device, consisting of a wire-gauze frame covered with 

 linen and thoroughly drenched with water, is inserted in the connection 

 between the mouthpiece or other breathing appliance used and the 

 circulating air.^ 



OXYGEN SUPPLY. 



If the whole apparatus is filled with air at the beginning of a period, 

 the percentage of oxygen in the confined air being breathed will fall 

 considerably and might easily reach the point at which oxygen-want 

 would be felt. Consequently, since the spirometer is of generous size, 

 and it has been established by Higgins^ that the respiration of oxygen- 

 rich atmospheres is without effect upon the gaseous metabolism, a hb- 

 eral supply of pure oxygen from a cylinder is introduced into the system 

 prior to connecting the mouthpiece with the subject and after an equiv- 

 alent volume of air has been expelled through the 3-way valve. During 

 the experiment the volume of air in the spirometer is decreased by 

 approximately 250 c.c. per minute, or 2.5 liters in a 10-minute period. 

 A rough calculation will indicate the probable amount of pure oxygen 

 to introduce. In the course of an experiment there is an exchange of 

 oxygen for nitrogen in the lungs and blood, so that the air in the system 

 contains a little more nitrogen than at first, but repeated tests have 



^ For a full description of these nosepieces, also method of use, see Carpenter, Carnegie Inst. 

 Wash. Pub. No. 216, 1915, pp. 22-23. 



^All workers in gaseous metabolism should refer to the monograph by Dr. T. M. Carpenter 

 (Carnegie Inst. Wash. Pub. No. 216, 1915) for detailed description of respiratory ap- 

 paratus of practically all the current types, with special reference on pp. 23, 36, and 37 

 to mouthpiece, nosepieces, and moistening device. 



' Benedict and Higgins, Am. Journ. Physiol., 1911, 28, p. 1. 



