40 MANUAL OF HISTOLOGY. 



absorption of water into cholic acid and glycin. Boiled with dilute 

 mineral acids, on the other hand, it yields choloidinic acid, C 24 H 38 4 , and 



glycin. 



Among its salts one in particular must 

 be borne in mind, namely, 



GLYCOCHOLATE OF SODIUM, C 26 H 42 IS"aN0 6 . 



(Fig. 19) a compound easily soluble in 

 water, which, precipitated from its solution 

 in alcohol by means of ether, crystallizes 

 in large, brilliant white stellate groups of 

 acicular crystals. 



This acid forms an essential constituent 



19,-Crystais of giycochoiate of human, as well as most mammalian 

 of sodium. bii e> j^ j s combined with sodium, even 



among the vegetable feeders. 



Taurocholic Acid, C 26 H 44 NS0 7 . 



This second acid is related very nearly, as regards its chemical consti- 

 tution, with the foregoing. It splits up, however, into cholic acid; 

 and (instead of glycin) taurin, an indifferent substance, containing sulphur, 

 and no longer basic. This is the amide of isethionic acid or sulfethylenic 



Taurocholic acid, which is very easily decomposed, is non-crystallizable, 

 but exceeds the last acid in its solubility in water and stronger acid 

 properties. It dissolves fats, fatty acids, and cholestearin with great 

 readiness. With sugar and sulphuric acid it gives the same reactions 

 as glycoholic acid. Its combinations with alkalies are very soluble in 

 alcohol and water, but insoluble in ether. Retained for a long period in 

 contact with ether, they crystallize. They burn with a brilliant flame. 



As regards the decomposition products of this acid, they are, as has 

 been already mentioned, analogous to those of the foregoing. On being 

 boiled with alkalies taurocholic acid splits up, on the absorption of water, 

 into cholic acid and taurin ; while, with the mineral acids, choloidinic 

 acid besides taurin is produced, analogously to the previous case. 



Combined with sodium taurocholic acid forms the second chief con- 

 stituent of the bile of man and numerous mammals, namely, tauro- 

 cholate of sodium, C 26 H 4;J NaNS0 7 . 



H. Amides, Amido-Acids, and Organic Bases. 



Under these names we have now to consider a series of further decom- 

 position products. 



Urea or Carbamide, CH 4 N 2 0, or CO j ^ 2 



Carbamide, which, like all the rest of the substances under considera- 

 tion here, is absent in the vegetable kingdom, but which forms, on 

 the other hand, the chief constituent of the urine of the human body, 

 is of perfectly neutral reaction corresponding in this respect with 

 kreatin, glycin, and leucin to be referred to presently. It crystal- 

 lises in long four-sided pillars, terminating at either end in two 

 facets (fig. 20). It is quite soluble in water and alcohol, but not so 

 in ether. 



