CONTAINED IN HUMAN BILE. 1G9 



unites with the elements of starch to form bile be 

 derived from the food or from the substance of the 

 metamorphosed tissues, the conclusion that its pre- 

 sence is an essential condition for the secretion of 

 bile cannot be considered doubtful. 



Since the herbivora obtain in their food only such 

 nitrogenised compounds as are identical in composi- 

 tion with the constituents of their blood, it is at all 

 events clear, that the nitrogenised compound which 

 enters into the composition of bile is derived from 

 a compound of proteine. It is either formed in 

 consequence of a change which the compounds of 

 proteine in the food have undergone, or it is pro- 

 duced from the blood or from the substance of the 

 tissues by the act of their metamorphosis. 



74. If the conclusion be accurate, that nitrogen- 

 ised compounds, whether derived from the blood or 

 from the food, take a decided share in the formation 

 of the secretions, and particularly of the bile, then 

 it is plain that the organism must possess the power 

 of causing foreign matters, which are neither parts 

 nor constituents of the organs in which vital activity 

 resides, to serve for certain vital processes. All nitro- 

 genised substances capable of being rendered soluble, 

 without exception, when introduced into the organs 

 of circulation or of digestion, must, if their compo- 

 sition be adapted for such purposes, be employed by 

 the organism in the same manner as the nitrogen- 

 ised products which are formed in the act of meta- 

 morphosis of tissues. 



