RESEARCHES BY OTHER INVESTIGATORS. 15 



expenditure in walking due to alterations in the number and length 

 of the steps. By means of a rubber bag and a Tissot mask, the air 

 expired during the experimental period was collected and samples 

 analyzed. The subject was in the post-absorptive condition and 

 walked with a carefully controlled frequency and length of step both on 

 a level and on grades of approximately 5, 10, and 15 per cent. Magne 

 found that the minimum net expenditure for a given distance on a 

 level was obtained at an approximate speed of 63 meters per minute, 

 and the average net efficiency for the grade experiments was not far 

 from 20 per cent. 



GENERAL CONSIDERATIONS WITH REGARD TO PREVIOUS WORK ON GRADE 



WALKING. 



The technical difficulties necessary to be overcome in a study of 

 grade walking are so great that only those who have had actual ex- 

 perience in such experiments are in a position to criticize fairly the 

 work of others. The historical development of the method of studying 

 metabolism during severe muscular work, not only that of walking but 

 likewise of other forms, such as bicycle riding, has gradually led to a 

 perfection of the technique. In reviewing the earlier work, it is 

 noticeable that the criticism that applied to the horizontal-walking 

 experiments applies with even greater force here, namely, that it 

 became necessary in many series of experiments to work under some- 

 what disadvantageous conditions. 



The dry gas-meter method, which has been used in so large a pro- 

 portion of the earlier studies, has one great disadvantage in that no 

 experiments can be made without a load. The carrying of a pack is 

 to be expected in walking, and particularly in Alpine work, but the 

 transportation of an apparatus such as a gas-meter and accessories, 

 weighing many kilograms and attached to the back, even though in 

 the most approved manner, still presents a problem in equilibrium 

 that is attained only with considerable practice. While it is true that 

 the transportation of loads is of great economic importance in indus- 

 trial operations, and a knowledge of the efficiency in transporting 

 loads is thus essential, yet thousands of people walk each day without 

 a load in comparison with the individual with a load; consequently, 

 observations which can be obtained on individuals not carrying loads 

 are, we believe, of general interest. 



The modern method of substituting either a Douglas bag or a 

 treadmill with a stationary meter is much to be preferred to the gas- 

 meter method, provided essential differences between the work of 

 walking in a well-ventilated room and that of walking in the free and 

 open air on an equally even or satisfactory path are not subsequently 

 developed. The Douglas-bag method is certainly a step in the right 



