360 TRYPTIC DIGESTION. [BOOK n. 



same way as pepsin is isolated, and to which the name trypsin has 

 been given. 



The appearance of fibrin undergoing pancreatic digestion is 

 however different from that undergoing peptic digestion. In the 

 former case the fibrin does not swell up, but remains as opaque as 

 before, and appears to suffer corrosion rather than solution. But 

 there is a still more important distinction between pancreatic and 

 peptic digestion of proteids. Peptic digestion is essentially an 

 acid digestion ; we have seen that the action only takes place in 

 the presence of an acid, and is arrested by neutralisation. Pan- 

 creatic digestion, on the other hand, may be regarded as an alka- 

 line digestion ; the action is most energetic when some alkali is 

 present ; and the activity of an alkaline juice is hindered or de- 

 layed by neutralisation and arrested by acidification at least with 

 mineral acids. The glycerine extract of pancreas is under all 

 circumstances as inert in the presence of free mineral acid as that 

 of the stomach in the presence of alkalis. If the digestive mix- 

 ture be supplied with sodium carbonate to the extent of 1 p.c., 

 digestion proceeds rapidly, just as does a peptic mixture when 

 acidulated with hydrochloric acid to the extent of -2 p.c. Sodium 

 carbonate of 1 p.c. seems in fact to play in tryptic digestion a 

 part altogether comparable to that of hydrochloric acid of -2 p.c. in 

 gastric digestion. And just as pepsin is rapidly destroyed by 

 being heated to about 40 with a 1 p.c. solution of sodium carbo- 

 nate, so trypsin is rapidly destroyed by being similarly heated 

 with dilute hydrochloric acid of *2 p.c. Alkaline bile, which 

 arrests peptic digestion, seems, if anything, favourable to tryptic 

 digestion. 



Pancreatic digestion and gastric digestion agree in that by 

 both proteids are converted into peptones. Naturally in the alka- 

 line pancreatic digestion no bye products allied to acid-albumin, 

 such as parapeptone, make their appearance ; there are however 

 various bye products on which we need not dwell. Albumoees 

 are not conspicuous in pancreatic digestion, they are very rapidly 

 carried on to the further stage of peptone. 



In one respect there is an essential difference between gastric 

 and pancreatic digestion. In gastric digestion the products are 

 not carried beyond the proteid stage ; in pancreatic digestion part of 

 the proteid is changed into something which is no longer proteid. 



During the pancreatic digestion of proteids, two remarkable 

 nitrogenous crystalline bodies, leucin and tyrosin make their appear- 

 ance. When fibrin (or other proteid) is submitted to the action of 

 pancreatic juice, the amount of peptone which can be recovered 

 from the mixture falls far short of the original amount of proteids ; 

 and the longer the digestive action, the greater up to a certain point 

 is this apparent loss. If a pancreatic digestion mixture be freed 

 from the bye products by neutralisation and filtration, the filtrate 

 yields, when concentrated by evaporation, a crop of crystals of 



