60 USES OF THE URINE 



lions, the use of which is to promote their passage 

 through the intestines, such as mucus. These excre- 

 ments contain no bile and no soda ; for water extracts 

 from them no trace of any substance resembling bile, 

 and yet bile is very soluble in water, and mixes with it 

 in every proportion. 



Physiologists can entertain no doubt as to the origin 

 of the constituent parts of the urine and of the bile. 

 When, from deprivation of food, the stomach contracts 

 itself so as to resemble a portion of intestine, the gall- 

 bladder, for want of the motion which the full stomach 

 gives to it, cannot pour out the bile it contains ; hence 

 in animals starved to death we find the gall-bladder dis- 

 tended and full. The secretion of bile and of urine 

 goes on during the winter sleep of hybernating animals ; 

 and we know that the urine of dogs, fed for three weeks 

 exclusively on pure sugar, contains as much of the most 

 highly nitrogenized constituent, urea, as in the normal 

 condition. (Marchaud. Erdmann's Journal fur prak- 

 tische Chemie, XIV. p. 495.) 



Differences in the quantity of urea secreted in these 

 and similar experiments are explained by the condition 

 of the animal in regard to the amount of the natural 

 motions permitted. Every motion increases the amount 

 of organized tissue which undergoes metamorphosis. 

 Thus, after a walk, the secretion of urine in man is in- 

 variably increased. 



The urine of the mammalia, of birds, and of am- 

 phibia, contains uric acid or urea ; and the excrements 

 of the mollusca, and of insects, as of cantharides and 



