X 



DIGESTION. 35 



Cholesterine is a product of waste taken up by the blood from the nervous 

 tissues and excreted by the liver. It crystallizes in the form of rhombic 

 plates, which are quite transparent. When retained within the blood, it 

 gives rise to the condition of cholesteramia, attended with severe nervous 

 symptoms. It is given off in the faeces under the form of stercorine. 



The Coloring matters which give the tints to the bile are biliverdin and 

 bilirubin, and are probably derived from the coloring matter of the blood. 

 Their presence in any fluid can be recognized by adding to it nitric acid 

 containing nitrous acid, when a play of colors is observed, beginning with 

 green, blue, violet, red and yellow. 



The Bile is both a secretion and an excretion ; it is constantly being 

 formed and discharged by the hepatic ducts into the gall bladder, in which 

 it is stored up, during the intervals of digestion. As soon as food enters 

 the intestines, it is poured out abundantly, by the contraction of the walls 

 of the gall bladder. 



The Amount secreted in 24 hours is about 2j^ pounds. 



Functions of the Bile, (i) It assists in the emulsification of the 

 fats and promotes their absorption. (2) It tends to prevent putrefactive 

 changes in the food. (3) It stimulates- the secretions of the intestinal 

 glands, and excites the normal peristaltic movements of the bowels. 



The digested food, the chyme, is a grayish, pultaceous mass, but as it 

 passes through the intestines it becomes yellow, from admixture with the 

 bile. It is propelled onward by vermicular motion ; by the contraction of 

 the circular and longitudinal muscular fibres. 



As the digested food passes through the intestines, the nutritious mat- 

 ters are absorbed into the blood, and the residue enters the large intestine. 



The Faeces consist chiefly of indigestible matters, excretin, stercorin 

 and salts; varying in amount from 4 to 7 oz. in 24 hours. 



Defecation is the voluntary act of extruding the faeces from the body ; 

 accomplished by a relaxation of the sphincter muscle, the contraction of 

 the walls of the rectum, assisted by the abdominal muscles. 



The Gases contained in the stomach and small intestine are oxygen, 

 nitrogen, hydrogen and carbonic acid. In the large intestine, carbonic 

 acid, sulphuretted and carburetted hydrogen. They are introduced with 

 the food, and also developed by chemical changes in the alimentary canal. 

 They distend the intestines, aid capillary circulation, and tend to prevent 

 pressure. 



