ABSORPTION. 37 



in the food. (3) It stimulates the secretions of the intestinal glands, and 

 excites the normal peristaltic movement 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, slercorin 

 and salts ; varying in amount from 4 to 7 ozs. 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. 



ABSORPTION. 



The term absorption is applied to the passage or transference of material 

 into the blood from the tissues, from the serous cavities, and from the 

 mucous surfaces of the body. The most important of these surfaces, espe- 

 cially in its relation to the formation of the blood, is the mucous surface of 

 the alimentary canal ; for it is from this organ that new materials are de- 

 rived which maintain the quality and quantity of the blood. The absorp- 

 tion of materials from the interstices of the tissues is to be regarded rather 

 as a return to the blood of liquid nutritive material which has escaped from 

 the blood vessels for nutritive purposes, and which, if not returned, would 

 lead to an accumulation of such fluid and the development of dropsical 

 conditions. 



The anatomical mechanisms involved in the absorptive process are 

 primarily, the lymph spaces, the lymph capillaries and blood capillaries ; 

 secondarily, the lymphatic vessels and larger blood vessels. 



Lymph spaces, Lymph capillaries, Blood capillaries. Every- 

 where throughout the body, in the intervals of connective tissue bundles, and 

 in the interstices of the several structures of which an organ is composed, 



