122 PHYSIOLOGY CHAP. 



0'2 per cent HC1, in which it has been standing in the cold 

 for 30 minutes. 



In order to compare the effect of the acidified splenic extract 

 with that of the plain hydrochloric acid on the raw fibrin, the 

 same amount of swollen fibrin is placed in two other flasks, with 

 15 c.c. of 4 per cent boracic acid, plus 15 c.c. of 0*4 per cent HC1. 



On placing the four flasks to digest in the oven at 39 C., the 

 fibrin with splenic extract is seen after two hours to be about half 

 digested, while that with hydrochloric acid alone shows no trace 

 of digestion. After 3| hours the other flasks are examined, and 

 the splenic extract is found to have digested almost all the fibrin, 

 while there is no trace of digestion in the fibrin left in the plain 

 acid solution. 



This fact, many times repeated in our laboratory by Lo 

 Monaco and Tarulli, proves that extract of congested spleen 

 contains pepsin, or at any rate an enzyme with an identical 

 capacity for digesting fibrin in an acid medium. The living 

 spleen probably contains not pepsin proper but some zymogen 

 capable of transformation into pepsin during the manipulations 

 necessary for the preparation of the extract. 



Hedin and Eowland (1901) further showed that the spleen 

 contains a proteolytic enyzme, which exhibits its maximal activity 

 in an acid solution. They also found it in many other organs 

 (lymph glands, kidneys, liver, and to a less extent the muscles 

 also ; infra, also Vol. I. p. 34). 



XV. Two kinds of glands are found in the mucous membrane 

 of the Intestine those of Brunner, which are confined to the first 

 portion of the duodenum, and those of Lieberkiihn, which extend 

 throughout the canal. 



The duodenal mucosa of certain rodents also presents groups 

 of cells which are structurally exactly like the acini of the pancreas 

 (particularly the duodenal pancreas described in rabbit). Accessory 

 pancreases in the duodenum are not uncommon in man. 



The mucous coat of the small intestine differs from that of the 

 stomach in having not only small ridges or folds that are obliter- 

 ated by distension, but also large permanent folds in the form of 

 crescentic projections of the mucous membrane, placed transversely 

 to the axis of the bowel, at a short distance from one another 

 (valvulae conniventes or valves of Kerkring). The whole surface, 

 including the valvular folds, is closely beset with villi, of varying 

 length, cylindrical in the jejunum, filiform in the ileum (Fig. 41), 

 which enormously increase the intestinal surface. The mucous 

 coat of the large intestine is smooth, and destitute of villi 

 (Fig. 42). 



Between the villi of the small intestine, in every part, are 

 the simple tubular glands, Lieberkiihn's crypts, which resemble 

 the fingers of a glove, the orifices being somewhat dilated at the 



