268 



I'lIYSIOUXJY 



CHAP. 



they are insoluble in ether (Heidenhain). Lastly, according to 

 Ramon y Cajal, the lymphoid tissue of the villi presents a very 

 fine plexus of nerves, the peripheral termination of the coarser 

 plexus of Meissner which is situated in the submucous layer of the 

 intestine (Fig. 91). 



The columnar epithelium with a striated border which clothes 

 the villi (see Fig. 43, p. 124) is apparently identical with that of 

 the crypts of Lieberkiihn, but the latter stains more intensely with 



various pigments, and its 

 border is much less plainly 

 striated. Moreover, the 

 nuclei of the latter often 

 exhibit mitotic division, 

 while karyokinetic figures 

 are never seen in the 

 epithelial cells of the villi. 

 These differences probably 

 indicate (as maintained 

 by A. D. Waller) that the 

 normal function of the 

 epithelium in the crypts 

 is the external secretion 

 of succus entericus, while 

 the epithelium of the villi 

 is an organ of absorption 

 and internal secretion of 

 the absorbed substance. 

 This removes the diffi- 

 culty which some physio- 

 logists find in admitting 



PIG. 91. Nerve endings from small intestine of guinea-pig. 



Potassium chromate and silver nitrate method. (Cajal.) 



a, b, c, /I, small nerve-cells belonging to the inter- 



glandular plexus of the mucous membrane; c, /, corre- 11 . oniil /-' 



spending cells belonging to nerve plexus of villi; M, Sam.6 CCllS, ITCtnSUttCtl'lOn 



ui-rvi- til ires belonging to Meissner's plexus, distributed orirl absorption "We shall 



find direct evidence for 

 this theory when we examine the absorption of fats in detail. 



Not only from the great extension of the absorbing surface, 

 but also from the various chemical digestive processes which the 

 chyme undergoes in the small intestine (owing chiefly to the 

 action of the various enzymes of the secretions poured into it), 

 absorption along the whole of this tract is more active than in the 

 stomach. Of this the case of duodenal fistula described by Busch 

 gives plain evidence. Although the patient was abundantly fed 

 by the mouth, she suffered continually from hunger, and in a few 

 weeks her weight went down so much that she was threatened 

 with death'from marasmus, which was only averted on feeding her 

 through the lower end of the fistula. In the cases of fistula at the 



opposite and simill- 

 ^ . ,, 



tanCOUS functions iOr the 



