CHAP, i.] TISSUES AND MECHANISMS OF DIGESTION. 455 



wall and their mouths carefully fastened in such a manner that each 

 mouth of the piece opens on to the exterior. During the process of 

 healing two fistulse are thus established, one leading to the beginning 

 of and the other to the end of a short piece of intestine quite isolated 

 from the rest of the alimentary canal ; by means of these openings a 

 small quantity of fluid can be obtained. 



The quantity secreted is increased by feeding the animal, that 

 is by setting up digestion in the stomach, and the rest of the ali- 

 mentary canal, though no food be placed in the loop itself; it is 

 also said to be increased by the administration of pilocarpin. 



Succus entericus obtained from the dog by the above method 

 is a clear yellowish fluid having an alkaline reaction. The solid 

 matter has been observed to vary from 1'5 to 2 p. c., including a 

 more constant contribution of about *5 p. c. sodium chloride and 

 5 p.c. sodium carbonate. It generally contains a certain quantity of 

 mucus. It is said to convert starch into sugar, and proteids into 

 peptone (the action being very similar to that of pancreatic juice), 

 to split up neutral fats, to emulsify fats and to curdle milk. It is 

 also said to convert rapidly cane-sugar into grape-sugar, and by a 

 fermentative action to convert cane-sugar 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 

 statements 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. 



The scanty secretion of the large intestine, when obtained free 

 from mixture with food or the contents of the small intestine, 

 appears to contain no digestive ferments at all ; as we shall see 

 later on, the changes which the food undergoes in this portion of 

 the alimentary canal are chiefly the results of the action of micro- 

 organisms. 



251. Gall-stones. Concretions, often of considerable size, 

 known as gall-stones, are not unfrequently formed in the gall 

 bladder, and smaller concretions are sometimes formed in the 

 bile passages. In man two kinds of gall-stones are common. One 

 kind consists almost entirely of cholesterin, sometimes nearly free 

 from any admixture with pigment, sometimes more or less dis- 

 coloured with pigment. Gall-stones 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 combination with calcium. Gall-stones of this kind are dark 



