I.— PHYSIOLOGY. 157 



trained, will provide the particular state of activity that we may require 

 at the moment ? Man at least will conform with our requirements, and 

 will maintain at request either rest or any degree or type of activity which 

 we may desire. What is more, he, though himself the subject of investiga- 

 tion, can help us to make our observations, and very often intelligent 

 co-operation on the part of the subject may render easy experimental 

 procedure which would otherwise be impossible. We gain, too, the 

 advantage of learning the subjective impressions of the person on whom 

 we are making our experiments. Everyone will admit the importance of 

 these impressions when studying the physiology of the sense organs, but 

 may they not be of value, too, in the investigation of other functions % 

 Indeed they may help us not infrequently to gauge the normality or 

 abnormality of the conditions under which we are working. The point 

 of view of the mere spectator is, after all, an impersonal one, and if it 

 can be amplified and perhaps corrected by reference to the feelings of the 

 subject so much the better. The investigation of life is too difficult a 

 task to allow us lightly to discard any method which may help us, and 

 if we confine our attention to the lower animals we do limit ourselves to 

 objective experience and renounce the possibility of assistance from 

 subjective impressions. 



Can my assertion that there is a definite advantage in doing experi- 

 ments on man be justified by the information that has already been gained 

 from investigations on the human subject ? Let me briefly discuss the 

 position. 



We know, it is true, not a little about the respiratory exchange of 

 animals, but we can fairly claim to know very much more about the oxygen 

 consumption, C0. 2 output and energy exchange of man. Data have been 

 obtained on man whilst resting, walking, running, pedalling a bicycle, 

 rowing, swimming, traversing the snow on ski or the ice on skates, per- 

 forming military exercises, hewing coal at the pit face or pursuing other 

 industrial occupations, and doing mental work — a fairly representative 

 collection of man's various activities in his daily life. 



Such information is not of mere academic interest ; it has not been 

 obtained solely to satisfy our idle curiosity ; it is fundamental to physio- 

 logy. We learn from it how greatly the oxygen requirements and the 

 energy output vary with changes in occupation — we find that the energy 

 output when walking at four miles an hour is five times as great as during 

 rest, and that the trained athlete may for a number of minutes maintain 

 an oxygen consumption not far short of twenty times the resting value — 

 and we begin to realize quantitatively something about the latent possi- 

 bilities in the respiration, circulation and other bodily functions which 

 must be called upon to adapt themselves from moment to moment to 

 meet such widely varying demands. Observations on the general 

 metabolism and energy exchange in man have played, too, a conspicuous 

 part in the development of our knowledge of the general principles of 

 dietetics and of the science of nutrition both of the individual and of the 

 nation. 



Research on the intact, or practically intact subject, naturally demands 

 methods of investigation of very different character from those direct 

 experimental methods which may be employed when full functional 



