■64 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



up olive oil and water together, and allow the mixture to stand ; the 

 finely divided oil globules soon separate from and float on the 

 surface of the water ; but if a colloid matter like albumin or gum is 

 first mixed with the water, the oil separates more slowly. A more 

 permanent emulsion is formed by an alkaline fluid, and especially 

 when a small amount of free fatty acid is being continually liberated ; 

 the acid combines with the alkali to form a soap ; the soap was 

 formerly stated to form a thin layer on the outside of each oil globule, 

 which prevented them running together again. This is not now 

 regarded as correct ; the oil globules are prevented from running 

 together because of difi'erences in the surface tension between them 

 and the surrounding fluid. Pancreatic fluid possesses, however, all 

 the necessary qualifications for forming an emulsion : — i. It is 

 alkaline; ii. It is viscous from the presence of proteid; iii. It has 

 the power of liberating free acids. 



4. Milk-curdling Fenneiit. — The addition of pancreatic extracts 

 to milk causes clotting, which differs in some of its details from the 

 curdling produced by rennin ; but this action can hardly ever be 

 called into play, as the milk upon which the juice has to act has been 

 already curdled by the rennin of the stomach. 



INTESTINAL DIGESTION 



The pancreatic juice does not act alone on the food in the intes- 

 tines. There are, in addition, the bile, the succus entericus 

 (secreted by the crypts of Lieberkiihn), and bacterial action to be 

 considered. 



The bile, as we shall find, has little or no digestive action by 

 itself, but combined with pancreatic juice it assists the latter in all 

 its actions. In our practical exercises we have already seen this is 

 true for the digestion of starch. It is also true for the digestion of 

 proteid, and very markedly so for the digestion of fat. Occlusion of 

 the bile-duct by a gall-stone or by inflammation prevents bile entering 

 the duodenum. Under these circumstances the faeces contain a 

 large amount of undigested fat. In some animals the bile contains 

 a ferment which is able to convert starch into sugar. The chief 

 value of the bile in digestion is to act as a solvent of fats and fatty 

 acids. This property it owes to the bile salts. 



The succus entericus has no action on fats or proteids, but it 

 appears to have to some extent the power of converting starch into 

 sugar ; its most important action, however, is due to a ferment it 

 contains called invertin, which inverts saccharoses — that is, it con- 

 verts cane sugar and maltose into glucose. The original use of the 



