Bodily Labour upon the Discharge of Nitrogen. 463 



in the same time, and nnder as far as possible similar conditions, 

 would represent equal amounts of work done, but a very little expe- 

 rience will suffice to show that such is not the case, and the results of 

 my own experiments will, I think, bear out this opinion. Although 

 accustomed from childhood to this particular form of exercise, and 

 though the actual distances walked in these experiments was almost 

 always well within my powers, I can say with truth that, measured 

 by my own sensations, I have never before so fully appreciated the 

 effect of what is called " training." For this reason, I have confined 

 myself strictly to the consideration of gross results. When the dis- 

 tances were short, the effect produced was exceedingly variable, and 

 in the final experiments of 1879 and 1882, when the labour was tole- 

 rably exhausting, all that we can say is, that the effect on the dis- 

 charge of nitrogen is beyond all doubt ; but that it bears no sort of 

 relation to the work done in previous experiments. 



In each succeeding walk the average pace per hour increased very 

 perceptibly, and yet I am confident that this increase of pace did not 

 by any means involve a proportional increase of internal work ; in 

 short, I gradually " got into training." I must confess that I see no 

 escape from this difficulty.; it might possibly be eliminated by con- 

 tinuing the investigations over a very long period of time and taking 

 daily a very large amount of exercise, until as it were the bodily 

 machinery had learned to work uniformly, and then suddenly in- 

 creasing it very considerably. In my own case, a daily walk of 30 

 miles, increased to 50 every tenth day, would express my meaning ; 

 and even if this were kept up for two months or more, I should expect 

 the effect of the longer marches to become less and less marked. 

 The gist of the whole matter is, that we have to deal with a machine 

 which has a most marvellous power of accommodating itself to the 

 work put upon it, and this introduces a factor into the investigations 

 of which we are at present wholly ignorant ; indeed, the problem is 

 thereby rendered so complicated, that the hope of findiug any expla- 

 nation of the phenomena observed is somewhat distant. As regards 

 this particular form of exercise, assuming that it is done under the 

 most favourable conditions, the following points must be considered 

 in interpreting the results : — 



(1.) The individual who is the subject of experiment. 



(2.) The distance walked. 



(3.) The pace. 



(4.) The load carried. 



(5.) The external conditions, such as temperature, &c. 

 Each must be carefully worked out in turn, and a very large 

 number of experiments made before we shall be justified in arguing 

 from the results obtained in one case to those of another. 



Nor is this all. Some men are, so to speak, much more economical 



