192 



ABSORPTION. 



Fig. 59. 



nating action, drawing the narrowed portions of intestine up and down, 

 as they successively enter into contraction or become relaxed in the 

 intervals. The effect of the whole is to produce a peculiar, writhing, 

 worm-like, or " vermicular" motion, among the different coils of intes- 

 tine. During life, the vermicular or peristaltic motion of the intestine 

 is excited by the presence of food undergoing digestion. By its action, 

 the substances which pass from the stomach into the duodenum are 

 steadily carried from above downward, so as to traverse the entire 

 length of the small intestine, and to come in contact successively with 

 the whole extent of its mucous membrane. During this passage the 

 absorption of the digested food is constantly going on. Its liquefied 

 portions are taken up by the villi of the mucous membrane, and succes- 

 sively disappear; so that, at the termination of the small intestine, 

 there remains only the undigested portion of the food, together with 

 the refuse of the intestinal secretions. These pass through the ileo- 

 csecal orifice into the large intestine, and there become reduced to the 

 condition of feces. 



The digested fluids taken up from the intestine are first absorbed by 

 the epithelial cells covering the surface of the villi, and are thence 



transmitted to the deeper por- 

 tions of their tissue. This pas- 

 sage of the products of diges- 

 tion through the substance of 

 the epithelial cells is difficult 

 of demonstration for perfectly 

 homogeneous liquids, but it 

 may be distinctly seen in the 

 case of the fatty matters of the 

 chyle. As already described, 

 the oleaginous matters of the 

 food are emulsified by diges- 

 tion, forming in the intestine a 

 white milky fluid, termed the 

 " chyle," which is entangled in 

 the folds of the mucous mem- 

 brane, and adheres to the sur- 

 face of the villi. In chyle 

 which is drawn either from the 



lacteal vessels or the thoracic duct, the fatty matter still presents itself 

 in the same condition, and retains all the chemical properties of oil. 

 Examined by the microscope, it is seen to exist under the form of fine 

 granules and molecules, varying in size from 2.5 mmm. downward, 

 which present the ordinary appearances of oil in a state of minute sub- 

 division. The chyle, therefore, does not represent the entire product of 

 the digestive process, but consists of the fatty substances, suspended by 

 emulsion in a serous fluid. 



The emulsioned oil has accordingly passed from the cavity of the 



CHYLE PROM COMMENCEMENT OF THORACIC 

 DUCT, from the Dog. 



