DIGESTION. 271 



The hydrolytic process only affects a very small 

 amount of the fats ; but the emulsification extends to 

 nearly the whole quantity present, the soaps formed in 

 the first process greatly facilitating the formation of the 

 emulsion. 



(3) The proteolytic enzyme, trypsin. This acts, like pepsin, 

 in digesting proteids ; it differs from the ferment of the 

 gastric juice, however, in acting best in an alkaline 

 solution, and in being more rapid in its action, especially 

 towards fibrin and elastin. In the pancreas itself little 

 or no trypsin exists, but a zymogen known as trypsinogen 

 occurs. This body, by the action of acids, water, 

 alcohol, or by the natural process of secretion, splits off 

 trypsin. 



There is some evidence of the existence of a milk-curdling 

 ferment in the pancreatic juice. 



Among the organic constituents of pancreatic juice two sub- 

 stances may be mentioned which are formed in the pancreatic 

 digestion of proteids. These are leucin amido-caproic acid 

 CH 3 .(CH 2 ) 3 CH(NH 2 ).COOH [or according to Fischer, a-amido- 

 isobutyl acetic acid, (CH 3 ) 2 CH.CH 2 .CH(NH 2 ).COOH] and 

 tyrosin para-oxyphenyl amido-propionic acid HO.C 6 H 4 .CH 2 . 

 CH(NH 2 ).COOH. 



They are crystalline compounds, the former very soluble, 

 the latter only slightly soluble, in water. They are both 

 readily soluble in acids or alkalies. 



Changes in the Intestines. As already stated, the intestinal 

 secretions are alkaline, and in such a medium bacteria can 

 readily flourish. Bacteria therefore are usually abundant after 

 the food has passed out of the range of the antiseptic gastric 

 juice. Bacteria effect various changes of a putrefactive 

 character. Carbohydrates undergo the lactic fermentation, 

 cellulose is split up into carbon dioxide and methane, while 

 butyric acid and even free hydrogen are also produced. Other 

 bacteria produce hydrolysis of fats, yielding valeric acid, 

 C 4 H 9 .COOH, or isobutyric acid, C 3 H 7 COOH = CH(CH 3 ) 2 . 

 COOH. 



Other microbes act upon the proteids, producing fatty acids 



