184 THE BILE. 



be separated by decantation and dissolved in water, it precipitates, 

 as in the case of pig's bile, by both , the acetate and subacetate of 

 lead. This might, perhaps, be attributed to the presence of two 

 different substances, as in ox-bile, one precipitated by the acetate, 

 the other by the subacetate of lead. Such, however, is not the case. 

 For if the watery solution be precipitated by the acetate of lead 

 and then filtered, the filtered fluid gives no precipitate afterward 

 by the subacetate ; and if first precipitated by the subacetate it 

 gives no precipitate after filtration by the acetate. The entire 

 biliary ingredients, therefore, of human bile are precipitated by 

 both or either of ttfe salts of lead. 



Different kinds of bile vary also 'in other respects; as, for ex- 

 ample, their specific gravity, the depth and tinge of their color, the 

 quantity of fat which they contain, &c. &c. We have already 

 mentioned the variations in color and specific gravity. The alco- 

 holic solution of dried ox-bile, furthermore, does not precipitate at 

 all on the addition of water ; while that of human bile, of pig's 

 bile, and of dog's bile precipitate abundantly with distilled water, 

 owing to the quantity of fat which they hold in solution. These 

 variations, however, are of secondary importance compared with 

 those which we have already mentioned, and which show that the 

 crystalline and resinous substances in different kinds of bile, though 

 resembling each other in very many respects, are yet in reality far 

 from being identical. 



TESTS FOK BILE. In investigating the physiology of any animal 

 fluid it is, of course, of the first importance to have a convenient 

 and reliable test by which its presence may be detected. For a 

 long time the only test employed in the case of bile, was that which 

 depended on a change of color produced by oxidizing substances. If 

 the bile, for example, or a mixture containing bile, be exposed in 

 an open glass vessel for a few hours, the upper layers of the fluid, 

 which are in contact with the atmosphere, gradually assume a 

 greenish tinge, which becomes deeper with the length of time which 

 elapses, and the quantity of bile existing in the fluid. Nitric acid, 

 added to a mixture of bile and shaken up, produces a dense preci- 

 pitate which takes a bright grass-green hue. Tincture of iodine 

 produces the same change of color, when added in small quantity ; 

 and probably there are various other substances which would have 

 the same effect. It is by this test that the bile has so often been 

 recognized in the urine, serous effusions, the solid tissues, &c., in 



