96 CHEMICAL COMPONENTS OF THE HUMAN BODY. 



cholic acid is not precipitated, when acids are added to fresh bile. When boiled 

 with alkalies, it is resolved into taurine and cholic acid ; and when boiled with 

 the mineral acids, into taurine and choloidic acid. Its formula, as deduced from 

 the composition of its salts, is 52C, 45H, IN, 2S, 140; and this, with an 

 additional equivalent of water, corresponds to cholic acid + taurine. The alka- 

 line taurocholates, which are the forms under which this acid exists in the bile, 

 dissolve readily in water and alcohol ; they have no reaction on vegetable colors, 

 and have a sweet taste with a bitter after-taste ; when heated, they melt and 

 burn with a bright smoky flame. Although they may be kept for some time 

 in solutions exposed to the air, without decomposition, provided they be pure, 

 yet they are very readily affected by the presence of certain nitrogenous sub- 

 stances, such as mucus; and taurine is then set free, with alkaline cholates and 

 choloidates. The substance now designated Taurine (formerly known as biliary 

 asparagine) is a very peculiar neutral compound, which crystallizes in colorless, 

 regular, hexagonal prisms, with four and six-sided sharp extremities. It is 

 hard, craunches between the teeth, has a cooling taste, resists the action of the 

 atmosphere, dissolves in 15 parts of water and 573 of dilute alcohol, and has 

 no action on vegetable colors. It dissolves, without undergoing change, even 

 at the boiling point, in the mineral acids, but forms no compounds with them ; 

 hence it cannot be properly considered as a base. . The most remarkable peculi- 

 arity in its composition is the large proportion of Sulphur which it contains, 

 this amounting to 25.6 per cent. ; and yet, notwithstanding that this substance 

 had been analyzed by Grmelin, Demaray, Pelouze, and Dumas, the presence of 

 this element was overlooked, until it was discovered by Redtenbacher. 1 It may 

 be made evident by the development of sulphurous acid, when taurine is in- 

 flamed in air; and in this manner, when the presence of one of the conjugated 

 biliary acids has been detected by Pettenkofer's test, it may be determined to 

 be the tauro-cholic. When taurine is boiled with caustic potash, it develops 

 ammonia, and leaves a residue consisting solely of sulphurous and acetic acids 

 in combination with potash. It is thought probable by Lehmann, that the 

 sulphur of Taurine already exists in an oxidized condition, since it cannot be 

 recognized in this substance by any of the ordinary fluid oxidizing agents. 

 Taurine has never been found in an isolated state in healthy bile, although, as 

 just now pointed out, it is set free by the spontaneous decomposition of the 

 tauro-cholates. It must undoubtedly be regarded as one of the products of the 

 metamorphosis of the albuminous tissues ; but of the mode in which it is gene- 

 rated, no account whatever can be given. 



70. The coloring matter of the Bile, or Bile-pigment, is a substance pecu- 

 liarly difficult to investigate satisfactorily, owing especially to the very small 

 quantity in which it occurs, and to its extreme instability. The most frequent 

 form under which it presents itself, is that of a brown, non-crystalline powder, 

 devoid of taste and smell, insoluble in water, very slightly soluble in ether, and 

 more so in alcohol, to which it communicates a distinct yellow tint ; this sub- 

 stance, the cholepyrrhin of Berzelius, the Mliphaein of Simon, constitutes a 

 large part of most biliary calculi, in which, however, it exists in a state of inso- 

 luble combination with lime. When it is dissolved in alkaline solutions, these, 

 which are at first of a clear yellow, become, by exposure to the air, of a greenish- 

 brown tint; and it is on this modification, the consequence probably of a higher 

 oxidation, that the well-known changes of color which occur in some of the 

 animal fluids are dependent. The yellow alkaline solution, when treated with 

 nitric acid, becomes first green, then blue (which hue, however, can hardly be 

 detected in consequence of its rapid transition into violet), and then red ; after 

 a considerable period, the red again passes into a yellow color, but the nature 



1 "Ann. der Chem. und Pharm.," band Ivii. pp. 170-174. 



