684 ANIMAL PHYSIOLOGY. 
THE SERIES OF BILE ACIDS, ETO. 
Cholic (cholalic) atid. C.4Hi0Os. 
It is the starting-point of the bile-acid series, and may be obtained 
pure in an amorphous or crystalline form, soluble in water. This acid 
is dextro-rotatory. It may occur in the large or small intestine and in 
the feeces. In jaundice it is in excess in the blood, tissues, and excre- 
tions, especially the urine. . 
Pettenkofer’s Test.—With sugar and sulphuric acid it gives a red- 
dish color, which may or may not require slight heat for its ‘production ; 
but it is important, tg remember that this reaction may be produced by 
other substances, so that the test is at best by itself a doubtful one. 
Glycocholic acid. CseH.s NOs. 
This is the principal acid of ox-gall; occurs also in that of man, but 
apparently not in the bile of carnivora. : 
This acid crystallizes in fine needles, soluble in water especially if 
hot, in alcohol, but not in ether. It has a strongly acid reaction. 
CuHwOs + CsNHsO. — H.O = CrcsHisNO.. 
Cholalic acid. Glycin, Glycocholic acid. 
Whether it is formed in the body in the manner indicated by the 
above equation is uncertain, as glycin has not as yet been obtained free 
from any tissue. This acid is best prepared from ox-gall. 
Taurocholic acid. C2sHisNSO:. 
Though found in ox-gall it is most plentiful in human bile, that of the 
carnivora, and especially in dog’s gall. 
It crystallizes in needles but not readily. It is soluble in water and 
alcohol, insoluble in ether. Its salts are also soluble in water. Tauro- 
cholic acid is a very insoluble substance. 
CrsHisNOWS = CoHi.Os + C2H:NO3S — HO. 
. Taurocholic acid. Cholalic acid. Taurin. 
Like’ the preceding, it is dextro-rotatory. 
Cholesterin. CasH.:.OH. 
Remarkable as the only free alcohol occurring in the human body. 
This substance may readily and in great abundance be extracted from 
the nervous tissues, but most easily from gall-stones, of which it forms a 
large part. It can be derived from other tissues, the blood and especial- 
ly bile. It may be obtained in white fine needles from solution in hot 
aleohol, ether, etc. The substance is leevo-rotatory. 
Test.—Strong sulphuric acid added to it in solid form and heated, or 
to its solution in chloroform, gives a bright-red color, which changes on 
standing. 
Bile-Pigments, 
Bilirubin. CicHisN20s. 
Tt makes up a great part of the pigment of the bile of the carnivora 
and perhaps of man. -It abounds also in gall-stones, from which it may 
be obtained, in either the amorphous or crystalline condition, by extract 
ing with chloroform and further treatment. "When heated with nitrous 
