PART I. 



INTRODUCTION. 



A practical application of thermodynamic principles that has inter- 

 ested economists and physiologists has been the problem of determining 

 the mechanical efficiency of the human body as a machine. Not only 

 were the earlier writers handicapped by an inability to determine accu- 

 rately the intake of energy by the body in food and drink a handicap 

 that has since been admirably overcome by the use of the accurate calori- 

 metric bomb but they were likewise handicapped by an inadequate 

 measurement of the mechanical output of the individual experimented 

 upon. A study of this subject, therefore, must divide itself into two 

 parts: first, the determination of the intake of energy, and second, the 

 measurement and computation of the amount of work done. The present 

 paper is concerned with the second of these two divisions. 



Without going into an extended historical discussion relative to this 

 subject, it may be said that the attempts to make computations of the 

 intake and output of energy have been very numerous and for the most 

 part extremely crude, those of the output of energy dealing usually with 

 the work of either the arms or the legs. Among the various methods used 

 for studying the amount of work done by the arm may be mentioned the 

 lifting of weights, the filing of cast iron, pulling up weights by means of a 

 rope, shoveling earth to a height of about 2 meters, pulling on an oar, 

 pumping water, hammering, turning a crank or winch, and the more ac- 

 curate method recently employed by Zuntz 1 of using a brake ergometer, 

 and Johansson 2 of raising weights. In tests with the leg-motion, the mus- 

 cular work has been for the most part confined to lifting the body to a 

 definite height by ascending a ladder or stairs, carrying weights up stairs, 

 wheeling a loaded wheelbarrow up an incline, walking on a treadmill, and, 

 more especially, riding a bicycle or an apparatus similar in form. 



In studying the muscular work in the leg-motion of bicycling, a special 

 apparatus has been extensively employed. One of the earlier types of 

 this machine was that described by Atwater and Benedict, 3 in which a 

 pulley attached to the armature shaft of a small dynamo was pressed 

 against the rear wheel of a bicycle; the current generated by this dynamo 

 as it revolved by the movement of the pedals was then measured. By 

 using the dynamo as a motor, the machine could also be calibrated. 



1 Zuntz, Archiv fur (Anat. und) Physiol., 1899, Suppl., p. 39. 



2 Johansson, Skand. Archiv fiir Physiologie, 1901, II, p. 273. 



3 Atwater and Benedict, U.S. Dept. Agr., Office Expt. Stas. Bui. 136, 1899, p. 30. 



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