128 



PHYSIOLOGY 



CHAP. 



Sisto showed that the mucous membrane of adult mammals, 

 which does not normally contain lactase, can produce this enzyme 

 after a diet containing a large quantity of lactose, extending over 

 several weeks. Birds, too, can be induced to secrete lactase by a 

 still longer period of alimentation. 



The glandular crypts of the large, unlike those of the small, 

 intestine do not secrete any digestive juice. The food -stuffs 

 introduced into the large intestine, after making an anus preter- 



naturalis, undergo no diges- 

 tive modification. It is 

 impossible, by any means, 

 to obtain any considerable 

 quantity of secretion from 

 this part of the gut. The 

 small amount that can be 

 obtained by little sponges 

 enclosed in wire capsules 

 introduced by the fistula 

 is clear, gelatinous, neutral 

 in reaction, laden with floc- 

 culi of mucus (Klug and 

 Koreck). Injections of pilo- 

 carpine, which exaggerate 

 all secretions of the gastro- 

 intestinal tube, change the 

 appearance of the mucino- 

 genous epithelial cells of 

 the large intestine, so that 

 they exactly resemble those 

 which line the crypts of 

 the small bowel (Fig. 45). 



FIG. 45. Glands of large intestine of rabbit. (Hoiden- This fact, noted by Heiden- 



tog rest' after c pious secreti n f mucus : B ' after hai n's pupils, shows that 



the glandular epithelium of 



the large intestine is more subject than that of the small bowel to 

 mucosal changes during rest, and that during secretory activity the 

 mucus formed is excreted, and the primitive cells which predomi- 

 nate in the small intestine are regenerated, by a new formation of 

 the cytoplasm which surrounds the nucleus. Secretion of mucus 

 (which is very useful in facilitating the expulsion of the faecal 

 matters, which harden in the last part of the intestine by 

 absorption of water) thus seems to be the only well-ascertained 

 function of the secretory cells of the mucous coat of the large 

 intestine. 



XVII. Little definite is known as to the dependence of the 

 intestinal secretion on the nervous system. According to Thiry 

 and others, stimulation of the vagus produces no effect. According 



