l88 REPORTS ON INVESTIGATIONS AND PROJECTS. 



Recognizing this lack of knowledge, an investigation has been begun in 

 this laboratory in the hope of supplying such information. Ordinary serv- 

 ings of food have been collected and weighed and a sample of the serving 

 saved for analysis. At some future time determinations will be made on 

 these samples of the heat of combustion, the nitrogen, and the carbohydrates. 

 It is hoped in this way to collect enough data so that with a knowledge of the 

 materials included in a meal and an idea of the size of the helpings, the 

 amount of energy in any given meal may be calculated, at least approximately. 

 In addition to the collection of samples for analysis, the compilation of pub- 

 lished analyses of cooked foods has been begun and will be continued. 



ANALYSES OP OUTDOOR AIR. 



The analyses of the outdoor air begun last year have been continued. 

 These have been made almost daily by means of the Sonden-Pettersson gas- 

 analysis apparatus, with which very accurate determinations of carbon 

 dioxide, oxygen, and nitrogen can be made. Occasionally variations have 

 been found in the oxygen content of the air which are not accompanied by 

 similar variations in the carbon-dioxide content. No cause has thus far been 

 ascertained for this variation, and it is planned to make an even more thor- 

 ough study of such variations in the coming year, supplementing the analyses 

 with very accurate controls to make sure that the differences are not due to 

 variations in the apparatus. The significance of oxygen in respiratory pro- 

 cesses and the almost universal use of the oxygen content of the air as a 

 constant fully justify the continuance of this most interesting meteorological 

 study. 



PUBLICATIONS. 



The following publications have been prepared and issued during the past 

 year: 



(i) A comparison of the direct and indirect determination of oxygen consumed by man. 

 Francis G. Benedict. Amer. Jour. Physiol., 26, p. 15. 1910. 



The great importance of knowing accurately the amount of oxygen con- 

 sumed by man has led to many attempts to make this determination indi- 

 rectly. By means of simple forms of respiration apparatus it is possible to 

 determine the carbon dioxide eliminated and the water vaporized. If accu- 

 rate records of the body-weight can be obtained, the oxygen consumed may 

 also be computed by the simple formula a = b + c — d, in which a is the 

 weight of the oxygen, b the weight of carbon dioxide, c the weight of water 

 vaporized, and d the loss in body-weight of the subject. While it is rela- 

 tively easy to determine with considerable accuracy the carbon dioxide elim- 

 inated, it is extremely difficult to determine the water vaporized, and the 

 errors incidental to the determination of changes in body-weight are ordi- 

 narily so great that it is practically impossible to use this method for the 

 accurate determination of oxygen. With the new respiration calorimeters 

 at the Nutrition Laboratory the determination of all the grosser factors of 

 metabolism — i. e., carbon-dioxide production, water- vapor elimination, oxygen 

 absorption, and, indeed, heat elimination — was extremely satisfactory. With 

 the installation of a special balance, the changes in body-weight could be 



