ORIGIN OF THE BILE. 137 



water, or of water, urea, and uric acid ; or by the sep- 

 aration from the elements of proteine of a compound 

 containing no nitrogen. The solution of such problems 

 becomes less difficult, when the problem to be solved, 

 the question to be answered, is matured and clearly put. 

 Every experimental decision of any such question in the 

 negative forms the starting-point of a new question, the 

 solution of which, when obtained, is the necessary con- 

 sequence of our having put the first question. 



39. In the foregoing sections, no other constituent of 

 the bile, besides choleic acid, has been brought into the 

 calculation ; because it alone is known with certainty to 

 contain nitrogen. Now, if it be admitted that its nitro- 

 gen is derived from the metamorphosed tissues, it is not 

 improbable that the carbon, and other elements which 

 it contains, are derived from the same source. 



There cannot be the smallest doubt, that in the carni- 

 vora, the constituents of the urine and the bile are de- 

 rived from the transformation of compounds of proteine ; 

 for, except fat, they consume no food but such as con- 

 tains proteine, or has been formed from that substance. 

 Their food is identical with their blood ; and it is a mat- 

 ter of indifference which of the two we select as the 

 starting-point of the chemical development of the vital 

 metamorphoses. 



There can be no greater contradiction, with regard 

 to the nutritive process, than to suppose that the nitro- 

 gen of the food can pass into the urine as urea, without 

 having previously become part of an organized tissue ; 

 for albumen, the only constituent of blood, which, from 

 12* 



