ORGANS OF THE BODY. 513 



The enormous colouring power possessed by this pigment is also a point 

 of great interest. Diluted to a million times its volume, it is still capable 

 of communicating a distinctly yellow tinge to a layer of fluid two inches 

 deep. Again, as is well known, a very small quantity in the blood 

 of jaundiced persons imparts a yellow colour to their skin and con- 

 junctiva. 



The pigment of fresh green bile is probably biliverdin, nearly allied to 

 the last. It is also developed in the other species of bile on their 

 becoming green. Dissolved in alkalies, it gradually assumes a brown tint. 



In decomposirg bile, another brown colouring matter is also to be 

 found, which, on the addition of acid, assumes a green colour. This is 

 probably biliprasin. 



We have already referred, as far as necessary, to the mode of generation 

 of the various colouring matters ( 37). 



Another colouring matter, also present in the urine, has likewise been 

 recently discovered in this fluid, to which the name of urobilin ( 53) 

 has been given (Jaffe). 



Besides these constituents, neutral fats are also present in the bile, 

 also combinations of fatty acids with alkalies, lecithin, with its two 

 decomposition products, glycero phosphoric acid and neurin or cholin, 

 cholestearin (p. 30), and mineral matters. The latter consist principally 

 of chloride of sodium, some carbonate and phosphate of sodium, phosphate 

 of calcium and magnesium, as well as traces of iron, copper, manganese 

 (p. 62). Fresh bile contains no sulphates ; these are, however, produced 

 in it by incineration and by the processes of putrefaction, from taurin, which 

 contains sulphur (p. 49). 



Of gases, the bile contains (dog) a small amount of oxygen, abundance 

 of carbonic acid, and some nitrogen (Pfluger). 



The proportion of these matters in the bile is usually higher than in 

 the other digestive fluids, but varies greatly, according as the bile remains 

 for a longer or shorter time in the gall bladder, where it undergoes a loss 

 of water by absorption. The percentage of solid constituents in the 

 human bile is generally estimated at from 9 to 17 (Frerichs, Gorup). 

 That from the ox contains from 7 to 11 per cent., that obtained directly 

 from the livers of dogs, cats, sheep, only about 5 per cent. (Bidder and 

 Schmidt). The bile of the Guinea-pig is still richer in water. The 

 organic matters in man amount, according to Frerichs, to about 87, or, 

 according to Gorup, to 93 per cent, of the dried residue. Among these 

 the combinations of sodium, with the two biliary acids, appear to pre- 

 ponderate greatly, while the proportion of fats and of cholestearin is 

 much less considerable. The percentage of mineral constituents is stated 

 by Gorup to be about 6*14 of the whole solid residue. 



The secretion of bile in the normal conditions of the system is con- 

 tinuous, 'but liable to vary considerably. It depends, in the first place, 

 on the nature of the alimentary matters taken into the system, being 

 most abundant after a meal of flesh mixed with fat, while it decreases 

 niter purely fleshy food, and is still less after an exclusively fatty diet. 

 A draught of water also increases its amount, and after the introduction 

 of food into the system, the quantity elaborated becomes larger and larger 

 for several hours. 



The quantity of bile produced in twenty-four hours varies in many 

 animals, and has besides been estimated differently by several observers 

 for one and the same animal. From 1000 to 1800 grammes is supposed 



