EXCREMENTITIOUS SUBSTANCES. 95 



rarely square octohedral crystals, which effloresce on exposure to the air ; it is 

 soluble in 750 parts of boiling water, and in 4000 parts of cold, and dissolves 

 very readily in alcohol, especially when heated. Its taste is bitter, leaving a 

 faint sweetish after-taste. It fuses at 383; if heated above that temperature, 

 it loses its atom of basic water, and is converted into choloidic acid; and if 

 heated to 554, it becomes converted into dysli/sin, a resinous substance having 

 no acid properties. These changes may also be effected by boiling cholic acid 

 with hydrochloric acid. The acid reaction of this substance is sufficiently strong 

 to redden litmus, and to enable it, with the aid of heat, to expel the carbonic 

 acid from solutions of the alkaline carbonates. The salts which it forms possess 

 a bitter, and at the same time a slightly sweet taste ; they are all soluble in 

 alcohol, but water dissolves only the cholates of the alkalies and of baryta. 

 The salts of choloidic acid are perfectly isomeric with those of cholic acid ; but 

 it is curious that the former acid is displaced even by carbonic acid, although 

 with the aid of heat it decomposes the carbonates. Cholic acid may be recog- 

 nized wherever it occurs whether combined with its adjuncts as a conjugated 

 acid, or metamorphosed into the choloidic by the excellent test devised by 

 Pettenkofer, founded upon its peculiar reaction with sugar and sulphuric acid ; 

 for if, to the fluid suspected to contain bile, there be first added a little solution 

 of sugar, and pure sulphuric acid be then added by drops, a yellowish color is 

 produced, deepening to a pale cherry, then to a carmine, and lastly to an intense 

 violet tint, if bile be present. This test may, therefore, be applied to determine 

 the presence or absence of the characteristic components of bile ; and we shall 

 hereafter notice some of the results of its application. When choloidic acid is 

 distilled with nitric acid, it yields the volatile acids of the butyric and succinic 

 acid groups, as does also oleic acid under similar treatment ; and it has been 

 recently pointed out by Schultze, 1 that oleine, when submitted to the bile-test, 

 presents nearly the same reaction as bile ; so that a special relation seems to 

 exist between them. Cholic acid does not naturally occur in its isolated state, 

 and can only be obtained by processes that have the effect of separating it from 

 the nitrogenous substances with which it is normally conjugated. The com- 

 pound of Cholic acid and Grlycine ( 33), termed by Lehmann Glycocholic acid, 

 but formerly known par excellence as the bilic or cholic acid, is the principal 

 organic constituent of the bile of most animals ; being united in that fluid with 

 potash and soda as bases, and not having a sufficiently strong acidity to prevent 

 its salts from possessing an alkaline reaction. This acid crystallizes in extremely 

 delicate needles, which remain unchanged at 277; it has a bitterish-sweet taste, 

 dissolves in 120.5 parts of hot water, and 303 of cold, and is readily soluble in 

 spirit. By prolonged boiling with alkalies or baryta-water, it is resolved into 

 cholic acid and glycine ; whilst, if boiled with concentrated sulphuric or mu- 

 riatic acids, it is resolved into choloidic acid and glycine. Its alkaline salts, 

 which form " crystallized bile," are very soluble both in water and spirit, 

 and separate from their alkaline solutions on the addition of ether, in large 

 glistening white clusters of radiating needles, resembling wavellite. These 

 burn, when heated, with a bright smoky flame. The formula of this acid is 

 52C, 42H, N, 110 -f HO; and, with the addition of another equivalent of water, 

 is exactly that of cholic acid -f- glycine. 



69. The other conjugated acid of bile, termed by Lehmann the Taurocholic 

 (but also named choleic acid, and formerly known as bilin), has not yet been 

 separated in a state of perfect purity, that is to say, free from glycocholic acid ; 

 it cannot be obtained in a crystalline state, and it is more soluble in water than 

 glycocholic acid, whilst its acid properties are far weaker. It dissolves fats, 

 fatty acids, and cholesterin in large quantities; and is thus the cause why glyco- 



Canstatt's "Jahresbericlit," 1850, p. 101. 



