306 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



While this action is undoubtedly caused by an enzyme, it has not been possible 

 to isolate the so-called "steapsin " in a condition of even approximate purity. 

 As a matter of fact also, ordinary extracts of pancreas, such as the laboratory 

 extracts in glycerin, do not usually show the presence of this enzyme unless 

 special precautions arc taken in their preparation. It would seem that steapsin 

 is easily destroyed. With fresh normal juice or with pieces of fresh pancreas 

 the fat-splitting effect can be demonstrated easily. One striking method of 

 making the demonstration is to use hutter as the fat to be decomposed. If 

 butter is mixed with normal pancreatic juice or with pieces of fresh pancreas, 

 and the mixture i> kept at the body-temperature, the several fats contained in 

 butter will be decomposed and the corresponding fatty acids will be liberated, 

 among them butyric acid, which is readily recognized by its familiar odor, 

 that of rancid butter. 'Flic action of steapsin, as in the case of the other 

 enzymes, is very much influenced by the temperature. At the body-temper- 

 ature the action is very rapid. The nature of the fat also influences the 

 rapiditv of the reaction; it may be said, in general, that fats with a high 

 melting-point are less readily decomposed than those with a low melting- 

 point. It has been shown, however, that even spermaceti, which is a body 

 related to the fats and whose melting-point is 53° C, is decomposed, although 

 slowlv and imperfectly, by steapsin. The fat-splitting action of the steapsin 

 undoubtedly takes place normally in the intestines, but it is cpiestiouable 

 whether all the fat eaten undergoes this process. In fact, it maybe said that 

 two views are taught at present regarding the digestion and absorption of 

 fats. According to the older view, only a certain small proportion of the fat 

 undergoes splitting, or saponification, as it is sometimes called. The remain- 

 der of the fat becomes emulsified by the products (fatty acids) formed in the 

 splitting, and arc absorbed in an emulsified condition as neutral fats. Accord- 

 ing to the more recent view. 1 all the fat is supposed to be acted upon by the 

 steapsin, with or without previous cmulsification, with the formation of 

 glycerin and fatty acids. These two products, the latter perhaps in part as a 

 soap formed by reaction with the alkaline salts of the intestine, are absorbed 

 in solution, and subsequently are recombined, probably in the substance of 

 the epithelial (ills, to form a neutral fat again. On both theories one of the 

 first results of the action of the steapsin is the formation of an emulsion, the 

 value of which on the first theory is that it brings the fat into a form in 

 which it can be ingested by the epithelial cells of the villi, while on the 

 second theory it consists in the fact that by subdividing the fat globules 

 minutely the completion of the process of saponification is hastened. On cither 

 view, therefore, emulsification is an interesting preliminary to the absorption 

 of fat, and some discussion of the nature of the process seems to be demanded. 

 Emulsification of Fats. — An oil is emulsified when it is broken up 

 into minute globules that do not coalesce, but remain separated and more 

 or less uniformly distributed throughout the medium in which they exist. 

 Artificial emulsions can be made by shaking oil vigorously in viscous solutions 

 1 Mo..re and Rockwood: Journal <>/ Physiology, 1897, vol. 21, p. 58. 



