DIGESTION 193 



neutral oil will undergo division into globules of microscopic size, which are 

 held in suspension in the soap solution, forming what has been termed an 

 emulsion, which is white and creamy in appearance. The cause of this 

 minute subdivision of the fat and the necessity for it is unknown. It may 

 be assumed that by virtue of the subdivision a greater surface is exposed to 

 the action of the pancreatic enzyme and the digestion of the fat thereby 

 facilitated. The action of the pancreatic juice may then be said to consist 

 in the cleavage of the neutral fats into fatty acids and glycerin, after which 

 the formation of the soap and the division of the fat takes place spontane- 

 ously. The enzyme which produces the cleavage of the neutral fats has 

 been termed steapsin or lipase. The extent to which the cleavage of the 

 fat takes place in the intestine has not been definitely determined. There are 

 some who think the amount is relatively small, while others consider that 

 it is large, practically all of the fat undergoing this decomposition, with 

 the formation of soap and glycerin prior to their absorption. 



The rapidity with which pancreatic juice in the presence of bile and 

 hydrochloric acid (under conditions such as are present in the duodenum) 

 can develop sufficient fatty acid to form an emulsion was determined by 

 Rachford to be two minutes. The activity of steapsin is thus shown to be 

 very great. 



According to Pavlov the relative amounts of the pancreatic enzymes 

 produced, are conditioned by the character and amounts of the food principles 

 consumed. Thus, if chyme contains an excess of either starch, protein, or 

 fat, there is a corresponding increase in the amount of either amylopsin, 

 trypsin, or steapsin produced. The pancreas apparently adapts its activities 

 to the character of the food. Though it is probable that each enzyme is a 

 derivative of a special zymogen, it is positively known that this is the case 

 only with trypsin. This enzyme is a derivative of the zymogen, trypsinogen, 

 the production of which is thought to be the special function of secretin. 



Intestinal Juice. This fluid is a product of the activities of the cells 

 lining the follicles or glands of Lieberkiihn. Owing to its admixture with 

 other secretions and to the profound disturbance of the digestive function 

 caused by the establishment of intestinal fistulas, this fluid has rarely been 

 obtained in a state of purity or in quantities sufficient for accurate analyses 

 or for experimental purposes. Its physiologic properties and functions are 

 therefore imperfectly known. Various attempts have been made by physi- 

 ologists, by the employment of different methods, to obtain this secretion. 

 The method usually employed is that of Thiry and Vella. This consists in 

 dividing the intestine at two places, about eight or ten inches apart, restoring 

 the continuity of the intestine, and then uniting the two ends of the resected 

 portion to the edges of two openings in the abdominal walls. The resected 

 portion, being supplied with blood-vessels and nerves, maintains its nutrition 

 and secretes a more or less normal juice. 



When obtained from a dog under these circumstances the intestinal 

 juice is watery in consistence, slightly opalescent, light yellow in color, 

 alkaline in reaction, with a specific gravity of i.oio. Chemic analysis 

 reveals the presence of proteins, mucin, and sodium carbonate. 



The intestinal juice obtained by Tubbey and Manning from a small 

 portion of the human intestine (ileum) was opalescent, occasionally brownish 

 in color, alkaline, and had a specific gravity of 1.006. On the addition of 

 IJ 



