372 CHEMISTR Y OF THE DIGESTIVE PROCESSES. 



a glycogen-like substance was present in the other inucins, which, on 

 boiling with a mineral acid, formed a reducing sugar ; this substance he 

 supposed to be absent in bile mucin, and hence no reducing sugar was 

 formed on heating it with a dilute mineral acid. 



Paijkull 1 afterwards proved that the mucin-like substance which 

 gives bile its viscidity really belongs to the nucleo-proteids. If bile be 

 precipitated with dilute acetic acid, the presence of the bile salts 

 prevents the precipitate from redissolving in excess, and so causes it to 

 simulate a mucin ; but if the bile salts are removed by dialysing, or by 

 precipitating the substance with alcohol, centrifugalising and quickly 

 redissolving in water, the precipitate readily redissolves in excess of 

 acetic acid, and in this respect resembles a nucleo-proteid and not a 

 mucin. Also, when the substance is precipitated by, and just redissolved 

 in, dilute hydrochloric acid, and theft subjected to peptic digestion, a 

 substance is precipitated, which by its percentage of phosphorus can be 

 recognised as similar to the nuclein yielded under like conditions by" 

 nucleo-proteids. These facts, together with the much higher percentage 

 of nitrogen (14 to 16 per cent.) than mucin which it contains, and its 

 failing to yield a reducing sugar on boiling with dilute mineral acids, 

 show the substance to be a nucleo-proteid and not a mucin. The quantity 

 of this substance present in bile is very variable but always small, 

 amounting in ox bile to about one per thousand. 2 



The bile salts. There are found in bile the salts of a number of 

 organic acids of complicated structure, which are closely allied to one 

 another ; these salts are collectively called the bile salts. They are not 

 found in health in appreciable quantity elsewhere than in the bile, and 

 usually occur as sodium salts, except in the bile of some sea fishes, in 

 which they are present as potassium salts. 



Since bile is so easily obtainable in quantity, it is not surprising that 

 it should early have attracted the notice of the physiological chemist. 

 Thenard, in 1809, working with ox bile, was the first to obtain any 

 scientific knowledge of the bile acids. He distinguished two com- 

 ponents in bile, one precipitated by acetate of lead, which he called 

 bile resin, and a soluble part, which he named picromel He seems 

 . to have roughly separated in an impure condition those two most 

 commonly occurring bile acids, which we know to-day as glycocholic and 

 taurocholic acid, by a method not widely differing from that most used 

 at the present time. He precipitated bile with neutral and basic acetates 

 of lead, and then extracted the precipitate with nitric acid ; the insoluble 

 part left behind, his resin of bile, was impure glycocholic acid. The filtrate 

 he reprecipitated with excess of acetate of lead, collected the precipitate, 

 and decomposed it by a current of sulphuretted hydrogen, thus obtaining 

 his picromel, which must have corresponded to impure taurocholic acid. 



In 1826, Gmelin published a memoir 3 in which is described a large 

 number of bile constituents; amongst them, one corresponding to 

 glycocholic acid, which he obtained in a crystalline form ; and another 

 substance, taurine, of which he was the discoverer, although he wrongly 

 supposed that it existed ready formed in the bile. The next important 

 advance was made by Demarcay, 4 who obtained a substance (Choleinsaure) 

 which yielded, on heating with acids, taurine and a resinous substance, 



1 Ztschr.f. physiol. Chem., Strassburg, 1888, Bd. xii. S. 196. 2 Paijkull, loc. tit. 



3 " Die Verdauung nach Versuchen." 



4 Ann. d. Chem., Leipzig, 1838, Bd. xxvii. S. 270. 



