DIGESTIVE FLUIDS. 



103 



that, in health, the essential constituents of the bile are not 

 to be found in the faeces, only the colouring matter is left; 

 also, dogs from which the bile is abstracted by a fistulous 

 opening, are remarkably ravenous. These facts seem to 

 point out that the bile, which acts as a narcotic poison when 

 introduced unchanged into the blood, is decomposed in the 

 intestine, and gives rise to innocuous products, which are re- 

 absorbed to nourish the body. The seat of this decomposi- 

 tion appears to be the great intestine ; for there the bile dis- 

 appears, and various substances are found which are obviously 

 derived from its constituents. Of these, two are crystalline, 

 viz., excretinj a carbonaceous substance containing sulphur 

 (Marcet), and stercorin, a body derived from cholesterin 

 (Flint). 



72. The great intestine has a smooth mucous membrane, 

 with tubular follicles like those of the small intestine, but 

 apparently having a different secretion. The details of the 

 processes which take place in this part of the alimentary 

 tube are but little understood. The bulk of the faeces 

 consists of matters which have resisted all digestive pro- 

 cesses, and always contains starch grains, muscular fibre, and 

 vegetable tissues, when these substances have formed part of 

 the diet. 



. 58. SECTION OF AN INJECTED TONSIL, a, a, Mucous membrane 

 of fauces; 6, a recess; c, c, c, closed follicles. 



73. Before leaving the consideration of the alimentary tube, 



