46 GRAHAM LUSK 



urea synthetically, and in 1837 Liebig and Wohler, working together, 

 described the decomposition products of uric acid. 



Carl Voit, writing in 1865, thus describes Liebig's services: 



All these chemical discoveries, to which Liebig so largely contributed, gave 

 him his fruitful conceptions concerning the processes* in the animal body. Be- 

 fore him the observations were like single building-stones without interrelation, 

 and it required a mind like his to bring them into ordered relation. It is a 

 service which the physiologists of our own day do not sufficiently recognize. In 

 order to appreciate this one has only to read physiological papers written before 

 the publication of his books and afterward in order to witness how his writings 

 changed the mental attitude toward the processes in the organism. The chemical 

 discoveries on which he based his conclusions were, in fact, matters of general 

 knowledge, but it was he who applied them to the processes of living things. 

 Scientific progress is determined by the establishment of correct interpretations 

 and the creation thereby of new pathways and problems. A school-boy has a 

 better knowledge of many things than the wisest man had formerly; and he 

 laughs at the ignorance of his forefathers because he does not understand the 

 history of the human mind. 



The man of science ought to realize the factors which have given him the 

 vantage which he holds. But there are textbooks on physiology in which the 

 chapters on the animal mechanism do not even mention the name of Liebig. 

 This anomaly is possible only for those who do not understand history, and who 

 hold only the new to be worthy of consideration. Liebig was the first to establish 

 the importance of chemical transformations in the body. He stated that the 

 phenomena of motion and activity which we call life arise from the interaction 

 of oxygen, food and the components of the body. He clearly saw the relation 

 between metabolism and activity and that not only heat but all movement was 

 derived from metabolism. He investigated the chemical processes of life and 

 followed them step by step to their excretion products. 



The following quotations from Liebig's (6) "Thierchemie" appear to be 

 significant cf his attitude (Cambridge, 1842 ; Braunschweig, 1846) : 



It is clear that the number of heat units liberated increases or decreases with 

 the quantity of oxygen given to the body in a given time through the respiratory 

 process. Animals which respire rapidly and are therefore able to absorb a great 

 deal of oxygen can eliminate a larger number of heat units than those which 

 have the same volume but absorb less oxygen. 



Of metabolism in fasting, he writes: 



The first action of hunger is a disappearance of fat. This fat is present 

 neither in the scanty feces nor in the urine, its carbon and hydrogen must 

 have been eliminated through the lungs in the form of oxygen-compounds. It 

 is clear that these constituents are related to the respiration. 



Oxygen enters every day and takes away a part of the body of the fasting 

 person with it. 



Martell found that a fat pig lived 160 days without food and .lost 

 120 pounds. 



