364 SUCCUS ENTERICUS. [BOOK n. 



into lactic acid, and this again into butyric acid with the evolution 

 of carbonic acid and free hydrogen. 



According to the above results, succus entericus is to be re- 

 garded as an important secretion acting on all kinds of food. But 

 even at the best, its actions are slow and feeble. Moreover many 

 observers have obtained negative results, so that the various state- 

 ments are conflicting. Besides, we have no exact knowledge as to 

 the amount to which such a secretion takes place under normal 

 circumstances in the living body. We may therefore conclude 

 that, at present at all events, we have no satisfactory reasons for 

 supposing that the actual digestion of food in the intestine is, to 

 any great extent, aided by such a juice. 



Of the possible action of other secretions of the alimentary 

 canal, as of the caecum and large intestine, we shall speak when 

 we come to consider the changes in the alimentary canal. 



212. Gallstones. Concretions, often of considerable size, 

 known as gallstones are not unfrequently formed in the gall 

 bladder, and smaller concretions are sometimes formed in the bile 

 passages. In man two kinds of gallstones are common. One kind 

 consists almost entirely of cholesterin, sometimes nearly free from 

 any admixture with pigment, sometimes more or less discoloured 

 with pigment. Gallstones of this kind have a crystalline structure, 

 and when broken or cut shew frequently radiate and concentric 

 markings. The other kind consists chiefly of bilirubin in combi- 

 nation with calcium. Gallstones of this kind are dark coloured 

 and amorphous. Less common than the above are small dark 

 coloured stones, having often a mulberry shape, consisting not of 

 bilirubin itself, but of one or other derivative of bilirubin. Gall- 

 stones consisting almost entirely of inorganic salts, calcic carbon- 

 ates and phosphates, are also occasionally met with. In the lower 

 animals, in oxen for instance, bilirubin gallstones are not uncom- 

 mon, but cholesterin gallstones are rare. 



A gallstone appears always to contain a more or less obvious 

 ' nucleus,' around which the material of the stone has been de- 

 posited, and which may be regarded as the origin of the stone ; 

 the real cause of the formation of the stone lies however in certain 

 changes in the bile, by which the cholesterin, or bilirubin, or other 

 constituent ceases to remain dissolved in the bile. But we cannot 

 discuss this matter here. 



