246 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



of speculation. It has been suggested that the soap forms a thin coating or 

 membrane round the small oil-drops, thus preventing them from uniting. The 

 splitting of the oil into small drops seems to be caused, in cases of spontaneous 

 em unification, by the act of formation of the soap that is, the union of the 

 alkali with the fatty acid in other cases by the mechanical shaking, or by these 

 two causes combined. The application of these facts to the action of the pan- 

 creatic juice normally in the small intestine is easily made. When the chyme, 

 containing more or less of liquid fat, comes into contact with the pancreatic 

 juice, a part of the oil is quickly split by the steapsin, with the formation of free 

 fatty acids. These acids unite with the alkalies and the alkaline salts present in 

 the secretions of the small intestine (pancreatic juice, bile, intestinal juice) to 

 form soaps. The formation of the soaps, aided, perhaps, by the peristaltic 

 movements of the intestine, emulsifies the remainder of the fats and thus 

 renders them ready for absorption. It has been suggested that the proteids 

 in solution in the pancreatic juice aid in the emulsification, but there is no 

 experimental evidence to show that this is the case. A factor of much more 

 importance is the influence of the bile. In man the pancreatic juice and the 

 bile are poured into the duodenum together, and in all mammals the two secre- 

 tions are mixed with the food at some part of the duodenum. Now, it has 

 been shown beyond question that a mixture of bile and pancreatic juice will 

 cause a splitting of fats into fatty acids and glycerin much more rapidly than 

 will the pancreatic juice alone. 1 This effect of the bile is not due to the 

 presence in it of a fat-splitting enzyme of its own : the bile seems merely to 

 favor in some way the action of the steapsin contained in the pancreatic secre- 

 tion. Bile aids the emulsification possibly in another way. To be efficient as 

 emulsifiers the fatty acids must form soaps. The alkaline salts of the pancre- 

 atic juice do not appear to be in a form in which they can be used readily 

 for this purpose. It is supposed that the alkaline salts of the bile (and the 

 intestinal juice) are therefore made use of. The mechanism of the absorption 

 of the emulsified fat and the importance of bile in this process will be described 

 subsequently. 



Intestinal Secretion. The small intestine is lined with tubular glands, 

 the crypts of Lieberkiihn, which are supposed to form a secretion of consid- 

 erable importance in digestion. To obtain the intestinal secretion, or succus 

 entericus, as it is often called, recourse has been had to an ingenious operation 

 for establishing a permanent intestinal fistula. This operation, which usually 

 goes under the name of the " Thiry-Vella fistula," consists in cutting out a 

 small portion of the intestine without injuring its supply of blood-vessels or 

 nerves, and then sewing .the two open ends of this piece into the abdominal 

 wall so as to form a double fistula. The continuity of the intestines is estab- 

 lished by suture, while the isolated loop with its two openings to the exterior 

 can be used for collecting the intestinal secretion uncontaminated by partially- 

 digested food. The secretion is always small in quantity, and it must be 



1 Nencki : Archiv fur experimentelle Pathologic u. Pharmakologie, vol. 20, 1886, p. 367 ; Katch- 

 ford: Journal of Physiology, 1891, vol. 12, p. 27. 



