384 HANDBOOK OF PHYSIOLOGY. 



changes take place: firstly, the oil or fat is split up into glycerin, and 

 its corresponding fatty acid; secondly, the fatty acid combines with the 

 alkali, to form a soap which is chemically known as stearate, oleate, or 

 palmitate of potassium or sodium. Thus saponification means a chem- 

 ical splitting up of oils or fats into new compounds, and emulsification 

 means merely a, mechanical splitting of them up into minute particles. 

 The pancreatic juice has been for many years credited with the posses- 

 sion of a special ferment, which was called by Claude Bernard steapsin, 

 and which is a lipohjtic or fat-splitting ferment. This ferment has not 

 been isolated, but its presence may be demonstrated by adding portions 

 of the fresh pancreas to butter or other fat and maintaining the proper 

 temperature. Its action is made manifest by the liberation of butyric 

 acid, which smells like rancid butter. 



The generally accepted theory is that only a small portion of the 

 fat which is eaten is thus changed into soap, and that the function of the 

 saponified fat is to assist in the emnlsiric.ation of the major part, a proc- 

 ess which is favorably influenced by the bile. The proper emulsifica- 

 tion of fat is a necessary preliminary to its absorption, for Avhei in 

 disease the entrance of the pancreatic juice or the bile to the intestine 

 is interfered with, the faeces contains a great excess of fat. 



Some recent experiments, however, tend to invalidate the emulsion theory and 

 to prove that the entire fat of the food is changed in the intestine into fatt}' acids, 

 and glycerine; that the fatty acids are entirely, or in part, changed to soaps; and 

 that these soaps, or the mixture of soaps and free fatty acids, are absorbed in solu- 

 tion. The chief facts favoring this view are that: (1) The action of steapsin is suf- 

 ficiently rapid to allow the saponification of a full fatty meal within the ordinary 

 period of digestion; (2) histological examination has never shown that fat particles 

 can pass into a columnar cell, and none have ever been found in tl.'e broad striated 

 border of the cell; (3) the fat globules found in columnar cells after a fatty meal 

 grow steadily larger as the period of absorption progresses, indicating that they are 

 deposited from solution; (4) the fatty acids are easily soluble in bile solutions, and 

 the solubility of the soaps is greatly increased by the presence of bile. The fat con- 

 stituents, according to this theory, are recombined in the columnar cells to form 

 neutral fats. 



Conditions favorable to the Action. These are almost precisely sim- 

 ilar to those which have been mentioned as favorable to the action of 

 the saliva, and the reverse. The secretion of the pancreatic juice ap- 

 pears to be, at any rate in some animals, e.g. , the rabbit and dog, almost 

 continuous; the flow, however, is not uniform, the amount increases 

 immediately after taking food, and the maximum is reached in from 

 one to one and a half hours, then the amount falls to about one-half, 

 after which a conspicuous rise occurs, and this is followed by a gradual 

 fall to the base line. The nervous mechanism of the pancreatic secretion 

 has only recently been discovered by Pawlovv. Increased flow of secretion 

 will occur on stimulation of the spinal bulb or cord, or of the gland it- 



