DIGESTION. 273 



lolytic ferment in the pancreatic juice which cannot be distinguished 

 from ptyalin, is called Amylopsin. 



(4. ) Pancreatic juice possesses the property of curdling milk, contain- 

 ing a special (rennet) ferment for that purpose. The ferment is distinct 

 from trypsin, and will act in* the presence of an acid (W. Roberts). It 

 is best extracted by brine. 



(5.) Oils and fats are emulsified and saponified ~by pancreatic secre- 

 tion. The terms emulsification and saponification may need a little ex- 

 planation. The former is used to signify an important mechanical 

 change in oils or fats, whereby they are made into an emulsion, or in 

 other words are minutely subdivided into small particles. If a small 

 drop of an emulsion be looked at under the microscope it will be seen to 

 be made up of an immense number of minute rounded particles of oil 

 or fat, of varying sizes. The more complete the emulsion the smaller 

 are these particles. An emulsion is formed at once if oil or fat, which 

 nearly always is slightly acid from the presence of free fatty acid, is 

 mixed with an alkaline solution. Saponification signifies a distinct 

 chemical change in the composition of oils and fats. An oil or a fat is 

 made up chemically of glycerin, a triatomic alcohol (see Appendix), and 

 one or more fatty acid radicles. When an alkali is added to a fat and 

 heat is applied, two 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 saponifica- 

 tion means a chemical 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 possession of a special ferment, which was called by Claude 

 Bernard steapsin, and which was supposed to aid in one or both of these 

 processes. It appears very doubtful, however, if either the mechanical 

 or the chemical splitting up of fats by the alkaline pancreatic juice is a 

 ferment action at all. 



Several cases have been recorded in which the pancreatic duct being 

 obstructed, so that its secretion could not be discharged, fatty or oily 

 matter was abundantly discharged from the intestines. In nearly all 

 these cases, indeed, the liver was coinci dentally diseased, and the change 

 or absence of the bile might appear to contribute to the result, yet the 

 frequency of extensive disease of the liver, unaccompanied by fatty dis- 

 charges from the intestines, favors the view that, in these cases, it is to 

 the absence of the pancreatic fluid from the intestines that the excretion 

 or non-absorption of fatty matter should be ascribed. 



Conditions favorable to the Action. These are similar to those 

 which are favorable to the action of the saliva, and the reverse (p. 



18 



