512 LECTURE XXII. 



the paths already trod. We must not forget, moreover, that the action of 

 the ferments, especially those of the cells, is extremely sensitively regulated. 

 It is entirely dependent upon certain definite external conditions, such 

 as, for example, the concentration relations. Every disturbance in this 

 direction must force the entire course of the cell-work into other channels 

 and quickly bring it to a halt. It is very important that digestion should 

 be considered, at present, in a broad sense rather than to attempt to 

 establish its significance in any definite direction. Only from this 

 standpoint are we able to comprehend the nature of digestion in its com- 

 pleteness, and from thence new ways and new goals appear for future 

 investigation in this infinitely complicated field. 



In the duodenum, the chyme first comes in contact with the alkaline 

 intestinal juices. The acid in the food mixture begins to be neutralized. 

 This juice is partly obtained from glands placed in the mucous membrane 

 at the beginning of the duodenum, and known as Brunner's Glands; but 

 the so-called Lieberkuhn's Glands are more important. These are found 

 in the mucous membrane of the entire small intestine. Even in the large 

 intestine similar little glands are found, although these differ in the nature 

 of the epithelium and in their functions from the corresponding glands 

 in the small intestine. 



The glands of Brunner have been considered by some as small pan- 

 creatic glands, while others have regarded them as similar to the glands 

 in the pyloric region of the stomach. The work of Pawlow and Parast- 

 schuk 1 makes it seem probable that these glands yield a ferment which 

 corresponds to pepsin. These investigators have shown, moreover, that, 

 like pepsin, this ferment requires hydrochloric, or some other acid, to acti- 

 vate it. The secretion from these glands also has a milk-coagulating action. 

 Here, in the same way as with regard to the juice of the pyloric region of 

 the stomach, it is possible to show that Pawlow's assumption is correct. 2 



The secretion from the glands of Lieberkuhn has been the object of 

 much careful investigation. It may be studied by the aid of a fistula, 

 made in the small intestine. It has been shown that starving dogs pro- 

 duce no secretion, or at least but very little. Secretion sets in when the 

 intestine is in any way irritated, whether by mechanical, chemical, or elec- 

 trical means. Ingestion of food also causes the secretion. The secretion 

 varies in different parts of the intestine. In the upper part it is less abun- 

 dant than in the lower. The juice of the intestine reacts alkaline, and 

 always contains sodium chloride and carbonate in apparently quite con- 

 stant proportions. According to recent investigations, it contains a fat" 

 splitting ferment, 3 and one with a slight amyolytic action. Furthermore, 



1 Z. physiol. Chem. 42, 415 (1904). 



8 Abderhalden and Rona: Z. physiol. Chem. 47, 359 (1906). 



3 W. Boldireff: Zentr. Physiol. 18, 460 (1905). 



