226 CONJUGATED ACIDS. 



crystals of various sizes, visible to the naked eye, and composed 

 either of cholate or glycocholate of soda. It is worthy of remark 

 that even the smallest quantities of the alkaline glycocholates crys- 

 tallise from their solution in this way. (From a solution of about 

 O07 of a gramme of glycocholate of soda in 150 parts of alcohol, 

 I obtained most beautiful crystals of the salt on the addition of 

 560 grammes of ether.) These crystals must, however, always be 

 examined microscopically, or at all events with a lens, as many 

 other salts (acetate of soda for instance) separate in a crystalline 

 form under this mode of treatment : they form six-sided prisms 

 with a single very oblique plane of truncation, and as their aqeous 

 solution reacts with Pettenkofer^s bile-test, no doubt can remain 

 regarding the presence of glycocholic acid. If the crystals be 

 obtained either in a state of purity or surrounded by syrupy 

 matter, we must separate the acid from the alkali by a little sul- 

 phuric acid, and extract with ether, in which the conjugated cholic 

 acids as well as choloidic acid are almost insoluble ; if the crystalli- 

 sable cholic or glycocholic acid be thus isolated, we can determine 

 regarding the presence or absence of one or other of them by boil- 

 ing with a solution of potash, when, if glycocholic acid be present, 

 ammonia is developed ; moreover, the cholate of baryta is a crystal- 

 lisable salt, while the glycocholate of baryta is amorphous. Gly- 

 cocholate acid resembles choloidic acid in being only slightly 

 soluble in ether ; they may, however, generally be distinguished by 

 the crystallisability of the former acid and of its salts fromethereo- 

 alcoholic solutions ; the glycocholate of baryta, indeed, resembles 

 the choloidate in being uiicrystallisable, but it differs from the 

 latter in being soluble in water. We shall point out the means of 

 distinguishing between glycocholic and taurocholic acids in our 

 observations on the latter acid. 



Physiological Relations. 



Occurrence. As far as our investigations have hitherto extended, 

 this acid has been found in the bile of all animals, with the excep- 

 tion of the pig. In reference to its occurrence in other parts and 

 fluids of the animal body, we have only to repeat what has already 

 been said in pp. 124-5 regarding cholic acid. We meet with such 

 minute quantities of biliary matter in the intestinal canal, in the 

 blood, and in exudations, that until recently they have been, for the 

 most part, entirely overlooked, and it is only by means of Petten- 

 kofer's admirable test that we can now detect them. Important as 

 it would be in a physiological point of view to ascertain whether 



