A HISTOKY OF METABOLISM 67 



why things are; in other words, the doctrines and the theories. It is 

 only later, when the young man has accumulated new facts out of har- 

 mony with the old theories, that those theories are overthrown and left 

 as wrecks by the wayside. That is the history of science. 

 Voit (&) has put the matter thus: 



I cannot agree with those \vho think that because they do not agree with 

 our conclusions they can overthrow the whole piece of work (that of Bischoff 

 and Voit). For even though our theories should be as bad as represented, the 

 important part of the work, the experimental results, would still remain. Those 

 who know the history of science should have no idle illusions over the value of 

 their own opinions. Upon every page of history one can read that, the results 

 of a properly devised experiment are immortal, whereas the theories drawn from 

 the observation are frequently shown to be wrong, because it was not possible 

 at the time to take into consideration all the factors at work during the experi- 

 ment. 



. . . From theories further scientific progress is evolved, they stimulate re- 

 newed activity. It often happens to the investigator that others with little 

 trouble to themselves present new conceptions of the work accomplished by him- 

 self, but the intelligent man, whose opinion and not that of the world in general 

 is worth while, will not forget to whom credit for the service belongs. 



An early work by Yoit, "Beitrage zum Kreislauf des Stickstoffs" may 

 be thus abstracted: In recent times one has sought to obtain a more 

 intimate knowledge of the metabolism in the animal body by comparing 

 the intake of various constituents of food with the constituents of the 

 outgoing substances. In this category belong the experiments of Bidder 

 and Schmidt and of Bischoff (1853). 



Bidder and Schmidt found in cats and dogs that almost all the nitro- 

 gen was eliminated in the form of urea. In one cat fed with meat 99.1 

 per cent of the ingested nitrogen was found in the urine, 0.2 per cent 

 in the feces, leaving only 0.7 per cent for the respiration. 



Barral taught from experiments on himself that 8.33 per cent of 

 the ingested nitrogen was eliminated in the feces, 42.07 per cent in the 

 urine, leaving over 50 per cent for elimination by the lungs, an amount 

 certainly too large in the light of recent exact determinations of the 

 nitrogen elimination in the respiration, especially in those of Regnault 

 and Reiset, who never found more than 1/50 and usually less than 1/200 

 part of the ingested nitrogen thus eliminated. Voit calculates that Reg- 

 nault and Reiset's dogs, which absorbed between 121 and 212 gm. of 

 oxygen daily, could have eliminated only between 0.04 to 3.69 gm. of 

 nitrogen gas in twenty-four hours. 



Both Lehmann and Boussingault, working with indirect methods, 

 found that much of the ingested protein nitrogen must have been elimi- 

 nated in the urine. 



Bischoff was the first to use the titration method of Liebig for the 

 determination of nitrogen in the urine. This method is exceedingly accu- 



