THE DIGESTION OF FAT 277 



tissue soluble in ether, as is shown by the fact that on saponifica- 

 tion the extract yields only about 60-65 per cent, of its weight 

 as insoluble fatty acids, while pure animal fat yields 95 per 

 cent. Glikin extracts with petrol-ether for 48 hours, and removes 

 lecithin by acetone, in which it is insoluble. This method ex- 

 tracts very little nitrogenous matter. The following are chemical 

 processes which are of value in investigations into the nature of 

 fats : 



(1) The acid number, which indicates the amount of free fatty 



N 

 acid. The alcohol-ether extract of the fat is titrated with JQ 



alcoholic potash, phenol-phthalein being used as indicator. 



(2) The saponification number, which indicates how many milli- 

 grams of KHO become combined with a fatty acid on treating 



N 

 1 grm. of the fat with -^- alcoholic potash solution. 



(3) The Reichert-Meissl number, which gives the amount of 

 volatile fatty acids. 5 grm. of the fat are saponified and then acidi- 

 fied with H SO 4 and distilled. The volatile fatty acids are caught 

 in standard alkali. 



(4) The iodine number, which gives the amount of iodine which 

 a weighed amount of fat will take up. It mainly indicates the 

 content of fat in unsaturated fatty acid, i.e. olein. 



THE DIGESTION OF FAT 



Fat undergoes no change in the mouth. In the stomach the 

 taking of fat tends to inhibit the secretion of gastric juice 

 (Pawlow). Neutral fats introduced as oil or fat into the stomach 

 of a man scarcely suffer any change, and yield after some hours 

 only 1-2-7 per cent, free fatty acid. On the other hand, finely 

 emulsified fats are split to a very large extent. Thus egg yolk 

 removed from the stomach after 1-4 hrs. was found to be very 

 strongly acid, and split to the extent of 78 per cent, into fatty acid 

 (Volhard). The finer the emulsion the more intimate the mixture 

 and the greater the action of the gastric lipase. In new-born 

 babies this lipase must play an important part, since milk is a fine 

 emulsion of fat, and the pancreatic juice is inactive at this early 

 age. Such assimilation of fat as takes place after the extirpation of 

 the pancreas depends largely on the action of the gastric lipase, and 

 thus the absorption is found to be much greater when milk or finely 



