A HISTORY OF METABOLISM 65 



The celebrated Pettenkofer reaction for bile salts was not determined 

 by accident. Liebig thought that fat arose from carbohydrate. To test 

 this, Pettenkofer treated a solution of cane-sugar with strong sulphuric 

 acid in order to dehydrate the sugar and obtain a rest rich in carbon 

 which might be convertible into fat. Since the liver or bile was believed 

 to further such a reaction. Pettenkofer added bile salts to the mixture and 

 obtained, n<>t fat, but the well-known color reaction. Using this reaction, 

 he was able to show that normal feces contained no bile salts, though these 

 might be found in diarrhea. 



In 1844 Pettenkofer found a compound in the urine which united 

 with zinc chlorid and he established its chemical composition. Its identity 

 remained hidden until it was one day shown to Liebig, who warmed it 

 over a flame on a porcelain cover, and from the odor evolved immediately 

 concluded that it must be related to the creatiu of muscle. Such is genius ! 



Voit, who was acquainted with the work of Bidder and Schmidt, sug- 

 gested to Pettenkofer that he devise a respiration apparatus which would 

 measure the output of carbonic acid and water in a dog weighing 20 to 

 30 kilograms. Pettenkofer, who was interested to work with men as 

 well as with dogs, constructed the chamber of the apparatus so that it had 

 the size of a moderately large stateroom on a steamer, in which a man 

 could sleep, work and eat without discomfort. ,The ventilation of the 

 chamber was about 500.000 liters daily. Portions of the ingoing air and 

 portions of the outgoing air were diverted in their course and analyzed 

 for carbon dioxid and water. The increase in these materials in the 

 total air leaving the chamber represented the amounts given off by the 

 subject of the experiment. This was the first respiration apparatus 

 checked by burning a candle in it. Pettenkofer criticized Kegnault and 

 Ileiset for not doing this, and thus establishing the limitations of the 

 accuracy of their work, a test which would have shown why nitrogen gas 

 was apparently at time? absorbed and at other times excreted by their 

 animals. 



Voit writes: "Pettenkofer's talents produced the respiration ap- 

 paratus and after that we together began experiments with it. Petten- 

 kofer and I hud an equal share in the experiments." 



Carl von Voit (1601-U.OS) was born in Amberg and was the son of 

 August Voit, architect of the Munich Glftspalftst. In 1848 he went to 

 Munich to enter the university. Ife joined a students' corps but soon 

 left it in disgust, feeling it was no place for him and perhaps reflecting 

 upon the German witticism, "Er war so dumm class selhst seine eigene 

 Corpsbriidern.es bemerckt haben." He entered enthusiastically into the 

 republican ideas prevalent in that year in Germany. His revolutionary 

 activities earned him a black mark on the qualifications list of the uni- 

 versity, a fact which he discovered long afterward when he had risen in 

 position and fame. 



