A HISTORY OF METABOLISM 55 



"Soup and pap were discovered because experience has taught mankind that 

 foods which are good for healthy people are not good for the sick." 



One need only compare the capacity for work of the German workman, who 

 lives on bread and potatoes, with the English or American workman, who eats 

 meat, in order to gain a clear insight into the importance of the kind of food 

 taken. The partaking of meat raises the capacity, the power and the endurance 

 for work. Or compare an English statesman who may speak for five hours or 

 more in a Parliamentary debate, and who in the full possession of youth may 

 still engage in a strenuous hunt at the age of sixty, with a German professor 

 of the same age who sparingly conserves the rest of his physical powers and 

 who is exhausted by a walk of a few hours. 



. Liebig cannot understand the modern expressions, "organized protein" 

 and "circulating protein" ; they confuse him to such a degree that he 

 cannot tell his right hand from his left. 



It is right to investigate a single phase in order to comprehend the existence 

 and activity of a whole process, but in order to interpret correctly the results of 

 investigations one must have a clear picture of the manifold phenomena and 

 the limitations affecting the entire problem. 



I have a general knowledge (Ich weiss so ziemlich) of how to estimate the 

 importance of experiments and facts, and of their inequality as far as draw- 

 ing conclusions is concerned. The simple observation of a natural phenomenon 

 arranged without our assistance is more important and often much more diffi- 

 cult than the phenomena observed in an experiment produced by our will. In 

 the first reality is mirrored, while an experiment represents the imperfection of 

 our understanding. 



I remember that many years ago during a walk between Berchtesgaden 

 and the Konigssee, a very simple observation led me to the conclusion of the 

 source of carbon in plants. At that time there was great confusion in the 

 subject, and it was difficult to exclude humus from consideration as a factor. 

 But on this walk Nature gave the proof that the carbon of the plant could arise 

 only from carbonic acid. For one finds rocks there which had been dislodged 

 and had fallen from the higher mountain side, and trees thirty or forty feet 

 high grow on the rocks, sending their roots between the crevices while the 

 rocks are covered only with moss and a layer of dust. It was impossible to con- 

 ceive that humus could have conveyed carbon to vegetation of this sort. 



Similar observations can be made in the laws of nutrition if one has but 

 the good- will to see them. 



It appears to me to be almost unthinkable that the high value placed by 

 the French family upon their "Pot-au-feu" is merely based on custom ; or that 

 one of the greatest military physicians of the French army, Dr. Baudens (Bau- 

 dens, 1857) would dare to say "La soupe fait le soldat" unless he was absolutely 

 convinced of the high potency of meat soup containing the necessary vegetables 

 which the French soldier often prefers to meat. 



Liehig laments the criticism of his extract of beef and quotes Goethe, 

 "The word of a wise man teaches me that if a person once does a thing 

 which is good for the world, the world takes pains to see that that person 

 does not do it a second time." 



One may annotate Liebig's opinion of Voit's "circulating protein" 

 and "organized protein" by citing a letter which Liebig wrote to Wohler 



