134 HUMAN PHYSIOLOGY 



those not capable of such splitting up are called antipep- 

 tones. 



(^) While pepsin digests collagen but not nuclein, trypsin 

 digests nuclein but not collagen. Gelatin, however, is 

 readily digested by trypsin. The gelatin peptones are not 

 split up by trypsin into amido-acids. Elastin is not digested 

 by pepsin, but readily by trypsin. 



(c) The products of proteid digestion by pepsin, injected into 

 the blood stream, stop the coagulation of the blood; not so the 

 products formed by tryptic digestion. 



(d) The rotatory power of the collective products formed by 

 peptic digestion is greater than that of the undigested proteid, 

 while the rotatory power of the products of tryptic digestion is 

 smaller. 



(e) In the presence of free hydrochloric acid, pepsin digests 

 trypsin, but in an alkali solution trypsin does not digest pepsin. 



Trypsin is not digested by pepsin in the intestine, because the 

 free hydrochloric acid, in so far as it is not united with the 

 proteoses, is neutralized by the alkali of the intestinal juices. 



During proteid digestion by trypsin the same intermediate 

 products arise as by peptic digestion. From coagulated 

 proteids there is formed in considerable quantities a soluble 

 proteid, coagulable by heat. Protalbumose and hetero- 

 albumose are not formed, but deuteroalbumose is directly 

 formed. 



To obtain trypsin for experimental work, heat the pan- 

 creas with highly dilute acetic acid and extract the ferment 

 with glycerin. Trypsin is not found in the pancreas in the 

 form of active ferment, but as zymogen. This zymogen is 

 transformed into the active ferment by dilute organic acids. 

 The secretion obtained by a pancreatic fistula often contains 

 only zymogen, which is converted into active trypsin by 

 coming into contact with the acid chyme. 



3. Action of steapsin. Steapsin of pancreatic juice is a 

 ferment which, by hydrolytic splitting up, changes neutral 

 fats into glycerin and free fatty acids. When alkali carbon- 

 ate is present in the intestine, soluble soaps are formed from 

 the fatty acids. 



It has not yet been determined to what extent fats are 



