90 Nutrition and Other Subjects of Allied Interest 



No. 166. BENEDICT, FRANCIS G. The Composition of the Atmosphere, with Special 

 Reference to its Oxygen Content. Octavo, m-f-115 pages, 1 plate. 

 Published 1912. Price $2.00. 



The object of this investigation was to obtain an exact knowledge of the com- 

 position of outdoor air, for in studying the character of combustion processes in the 

 body such knowledge is essential for the interpretation of the changes in the com- 

 position of air as it passes through the lungs. The first part of the publication con- 

 sists of an extensive review of the earlier literature on the subject and a history of 

 air analysis. The second part gives a description of a gas-analysis apparatus devised 

 by Dr. Klas Sonden, of Stockholm, together with the technique of its use and the 

 results of a series of analyses of outdoor air made at the Nutrition Laboratory 

 during a period of nearly three years. The steps in the elimination of individual 

 errors in the technique and routine are carefully traced, and the conclusion is reached 

 that uncontaminated outdoor air in Boston is of constant oxygen content, irrespec- 

 tive of conditions of weather, humidity, temperature, barometer, wind direction, 

 etc. Further analyses of air taken from many points on the Atlantic Ocean, and 

 from the top of Pike's Peak, showed a like uniformity in composition. 

 No. 167. BENEDICT, FRANCIS G., and WALTER G. CADY. A Bicycle Ergometer with 

 an Electric Brake. Octavo, m-f-44 pages, 16 text figures. Published 



1912. Price $0.50. 



A form of stationary bicycle, in which the rear wheel is replaced by a copper disk 

 rotating in an electro-magnetic field, has been extensively used in this laboratory 

 for measurements of the mechanical work of man. Certain important calibration 

 tests, friction measurements, and the peculiar magnetic reaction produced by the 

 copper disk rotating between the poles of the magnet are described in this publica- 

 tion. Two instruments were used, one having been calibrated several years before. 

 The new calibration of this latter instrument showed essentially the same values 

 as the earlier tests. The speed usually assumed by a bicycle rider ranges from 60 

 to 90 revolutions per minute, and at these speeds the ergometer, singularly enough, 

 gives essentially the same heat per revolution ; at slower and higher speeds there is 

 a marked decrease in the heat per revolution. A careful study of the magnetic 

 reactions in the disk showed the peculiarly interesting demagnetizing effect of the 

 eddy currents in the disk. 



No. 187. BENEDICT, FRANCIS G., and E. P. CATHCART. Muscular Work: A Meta- 

 bolic Study -with Special Reference to the Efficiency of the Human Body 

 as a Machine. Octavo, 176 pages, 1 plate, 10 text figures. Published 



1913. Price $2.50. 



This investigation, which was carried out by means of a special form of respi- 

 ration apparatus and the bicycle ergometer described in an earlier publication (Pub- 

 lication No. 167 of the Carnegie Institution of Washington), considers two essen- 

 tially fundamental questions first, the character of the material burned in the body 

 before, during, and after muscular work, and second, the relationship between the 

 amount of productive effective muscular work and the total heat output, this com- 

 parison indicating the mechanical efficiency of the human body as a machine. The 

 investigation lasted several months and involved several hundred experiments. 



It was conclusively demonstrated that during severe muscular work there is a 

 distinct alteration in the character of the materials burned in the body, as the evi- 

 dence indicated a selective combustion of carbohydrate material, though the experi- 

 ments do not point to an exclusive combustion of carbohydrate during muscular work. 



The major portion of the experiments was devoted to a study of the relationship 

 between the total heat output and the effective external muscular work, thereby 

 giving information in regard to the mechanical efficiency of man. An extensive dis- 

 cussion of what is meant by "gross" and "net" efficiency, together with the careful 

 computation of the maximum efficiency, leads to an interesting discussion as to the 

 analysis of the chemical and thermal processes involved in severe muscular work 



The report also considers other important questions relative to the muscular 

 work of man, such as the effect of muscular work on the pulse-rate, the body- 

 temperature, the mechanics of respiration, and the drafts upon the body material. 



