296 TRANSACTIONS OF SECTION I. 



This devious mode of progress, perhaps more marked in the work of 

 previous generations, is still manifest in many of the modern lines of advance, 

 largely as a result of too ready acceptance of the conclusions arrived at from 

 insuttieient experimental data. Witness the to-and-fro swing of our conception 

 of the significance of adrenalin in the body. The older workers were so ham- 

 pered by insufficient methods that many of the conclusions accepted as final 

 should have been taken as simply provisional. 



II. Protein IMetabglijm. 



A consideration of the present position of our knowledge of the metabolism 

 of protein in the body, and of the way in which we have arrived at it, is a 

 striking illustration of this zigzag advance, what I have elsewhere described 

 as tacking to windward. 



It was only towards the end of the eighteenth century that the true nature 

 of the nitrogenous constituents of plants and animals was recognised, although 

 ]>oerhaave in 1732 had indicated their identity. Fourcroy and Scheele and 

 Berthollet did much to advance our knowledge of their composition. 



1. Proteins as a Source of Energy. 



It was Liebig, early in the nineteenth century, who really first emphasised 

 the primary importance of the albuminous constituents of the body. It was he 

 who first clearly taught the value of these proteins as constituents of the food 

 in building up the living body. It was he who first pointed out that by their 

 combustion in the body the energy required for work is liberated — although he 

 made the mistake of concluding that it was all supplied by proteins. 



Is it to be wondered at that in those days of inadequate knowledge of 

 physiology and of imperfect methods of investigation, he had to content himself 

 with a purely theoretical consideration of the subject, and that he failed to 

 disabuse his mind of the idea of the necessary co-operation of some vital force 

 or spirit to protect the albumin from oxidation during the resting state of 

 muscle? Physiologists even at the present day are too apt to seize upon such 

 metaphysical abstraction as a cloak for ignorance ! 



The formulation by Liebig of the theory that the oxidation of proteins is the 

 sole source of the energy liberated in muscular work is perhaps the most striking 

 example of the danger of the bold statement by a great scientific authority of a 

 conclusion unverified by experiment. For years it dominated all study of the 

 physiology of nutrition and to the present day it influences the practice of trainers 

 of athletes. It was in vain t"hat Voit recorded his experiments, which showed that 

 muscular work does not increase the output of urea, which it should have done 

 had Liebig's theory been correct. Certainly Volt's experiments were themselves 

 imperfect, since he failed to carry his observations beyond the day in which 

 exercise was taken. 



It is a striking commentary on the credulity of physiologists that the 

 experiment which struck the first blow at the general acceptance of Liebig's 

 teaching was that of Fick and Wislicenus in their ascent of the Faulhorn, an 

 experiment which for years held a prominent place in every textbook of 

 Physiology, an experiment which every physiologist of to-day will agree was 

 absolutely wortliless, inasmuch as these observers took protein food on the day 

 before the experiment and were excreting its products next day, inasmuch as 

 they stopped collecting the urine on the night of the ascent, and inasmuch as 

 their estimation of the work done left out of consideration the respiratory 

 disturbances in the ascent. 



Rtill, I remember how, as a student, I was taught that this experiment had 

 overthrown the teaching of Liebig. Its influence is shown by the fact that 

 Pfluger took up the defence of Liebig's teaching. You all remember the 

 records of the very lean dog fed on the leanest horse-flesh in Bonn and doing 

 work in drawing a load the energy for which was liberated from proteins— 

 because the dog had nothing else from which to liberate it ! 



You all remember the -well-known experiment of Argutinsky by which he 

 thought to show that over 90 per cent, of the energy of the work of hill- 

 climbing came from proteins. At that time I ventured to point out that 



