238 



DIGESTION. 



[CHAP. xxv. 



push water through an obstructed syringe, the piston of which 

 is perforated in the centre, as illustrated by the 

 annexed woodcut (fig. 168).* 



The contents of the intestine are moved on, por- 

 tion by portion, much as in oesophageal deglutition. 

 And, in their progress, they are mingled with fluids 

 poured out from the intestinal mucous membrane. 



Changes in the Mucous Membrane during Intes- 

 tinal Digestion. During intestinal digestion the 

 mucous membrane exhibits an increased nutrient 

 activity, as evinced by a greater afflux of blood, 

 and by free secretion, as well as absorption ; in 

 connection with which last function it exhibits 

 peculiar changes, which must be specially noticed. 

 It is red, moist, and covered with a more or less 

 abundant mucus, etc. 



The most remarkable change which takes place 

 in the mucous membrane of the intestinal canal 

 is observed in that portion of it which is covered 

 by villi ; that is, throughout the small intestine, 

 especially below the point of entrance of the 

 hepatic and pancreatic ducts, The villi are the 

 agents of a peculiar process of absorption; and 

 the changes which take place in them at this 

 period appear to have immediate reference to the 

 part which they perform in this function. They 



Diagram to illustrate 7 i -i - , . T 



the formation of a back- become enlarged and turgid, partly owing to an 



ward axial current, in . -i JY\ n -\ i i , i 



pushing water through increased afflux or blood, to them, and partly in 



an obstructed syringe f , 1-1,1 i ,1 



with a piston perforated consequence oi a change which takes place in the 

 intra-villous tissue, whereby the component nuclei 

 and granules acquire an increase of size, and some of them arrange 

 themselves in lines passing from the extremity to the base of 

 each villus (fig. 160, A). These lines appear to proceed from an 

 accumulation of small cells formed at the free extremity of the 

 villus within its cavity (fig. 160, B b) : they are quite opaque, and 

 their structure is, therefore, impenetrable to high powers in the 

 microscope : they coalesce at the base of each villus, beyond which 

 we have not succeeded in tracing them.f 



* Contributions to the Physiology of the Intestinal Canal, loc. cit., a highly 

 ingenious and interesting paper. 



t The phenomena here described were observed in dogs and cats fed in 

 ordinary way upon meat, milk, etc. 



