INTRODUCTION. 9 



A second method involves the attachment of certain breathing appli- 

 ances, either nosepieces or mouthpiece, with an apparatus for meas- 

 uring the volume of the expired air. When the breathing appliances 

 have been adjusted, the subject assumes a certain body position and 

 then walks along a movable path, such as a treadmill. This method 

 was frequently used by Zuntz and Durig and their co-workers. 



A modification of this method is that in which the apparatus for 

 measuring and sampling the expired air is carried upon the back of the 

 subject, somewhat as a knapsack would be carried. The subject is 

 then no longer confined to walking upon a treadmill, but may walk 

 on level ground anywhere. This method was used extensively by 

 Zuntz and Durig and their associates and by Douglas. Instead of 

 having the apparatus carried by the subject, it may be transported 

 by an assistant walking a suitable distance behind him. The subject 

 thus breathes through the nose or mouth appliance, but is not obliged 

 to support the heavy apparatus. This method was employed by Burgi, 

 Schnyder, and, in certain experiments, by Kolmer and Brezina. 



Finally, it is possible to have the gas measuring and sampling appa- 

 ratus in a fixed position and the subject attached to it by a long tube. 

 He then walks in a clearly defined path, either back and forth across the 

 room or in a circle of which the apparatus is the center. This method, 

 which obviously limits appreciably the distance to be covered and the 

 general freedom of the subject, has found slight use with certain French 

 observers, particularly Amar. 



FUNDAMENTAL PRINCIPLE OF STUDYING THE GASEOUS EXCHANGE 



INCIDENTAL TO WALKING. 



The method of superimposition is the only one feasible for these 

 studies. By this method the gaseous exchange during walking in dif- 

 ferent positions must be carefully studied by one or more of the methods 

 previously referred to; subsequently, in order to apportion specifically 

 the energy transformation due to walking, it is necessary that a certain 

 part due to the metabolism of maintenance be subtracted from the 

 result obtained for the total gaseous exchange. 



The exact selection of the amount of energy transformed for main- 

 tenance to be deducted from the total energy transformation has been 

 a matter of considerable discussion. We have now come to realize that 

 a human individual may subsist on numerous metabolic levels. The 

 subject sound asleep, without food in the stomach, has a minimum 

 metabolism, but is utterly incapable of intellectual or physical activity. 

 It would obviously be impracticable, if not indeed undesirable, to 

 deduct this minimum metabolism from the measurement of the total 

 metabolism and assume that the difference would be wholly due to 

 the energy transformation due to walking. Even when the subject 

 is lying awake, we still have a base-line which is far removed from the 



