

ABSORPTION. 59 



act is the pressure of the abdominal muscles upon the contained 

 viscera, while the reflex is an increased peristalsis in the sigmoid 

 flexure and rectum and the relaxation of the sphincter. The centre 

 which governs this act, so far as it is reflex, lies in the lumbar 

 region of the spinal cord. 



ABSORPTION. 

 What is absorption? 



The digested food is taken from the intestines and carried into 

 the blood, whence it is taken to nourish the cells. This process 

 we know as absorption. The same term is applied to the removal 

 of worn-out material from the tissues. 



By what channels is food absorbed from the intestines ? 

 By the blood-vessels and lymphatics. 



What property of chyle renders it fit for absorption ? 



The property of passing through animal membranes. Chyle is 

 the name given to food after digestion. By digestion the proteids, 

 starches, and fats, which were not dialyzable. have become pep- 

 tones, sugars, and emulsified fat. All these products of digestion 

 are readily capable of dialysis, and therefore ready for absorption. 



What is dialysis? 



By dialysis we mean the property of fluids which enables them 

 to pass through animal membranes osmosis. This we have seen 

 is possessed in a high degree by the ingredients of chyle. The 

 reverse process may occur, and fluids (serum) from the blood may 

 similarly be drawn into the intestinal canal, as is seen when the 

 salines are used as purgatives. 



What anatomical features of the gut favor absorption ? 



(1) The valvulffl conniventes greatly increase the area of the 

 intestinal surface, and by their shelf-like formation delay the ad- 

 vance of chyle. (2) The villi of the intestine not only increase 

 the area, but are the special organs of the function of absorption. 

 (3) The contraction of the intestine upon its fluid contents also 

 favors, mechanically, the filtration of the contents through its walls. 



What are the villi? 



The villi are almost innumerable, minute, teat-like projections 

 from the surface of the wall of the intestine. They are very 

 numerous in the small intestine, and none are found in the large 



