172 PHYSIOLOGY CHAP. 



albumin. Since by Schut/.' l;i\v the rate of digestion or amount of protein 

 dissolved in the time unit are proportional 1o I lie square root of the quantity 

 of ferment, the quantity of pepsin or trypsin contained in (lie specimen 

 investigated must equal tlie square of the length of the column of egg-white 

 which it has digested in the given period. Supposing, c.;/., tliat the gastric 

 juice .1 dissolves a column of albumin of 2 mm. while the juice B dissoh <> 

 of 3 mm., it follows that the amount of pepsin present is as 4 : 9. 



(<') The presence of the digestive products, particularly of 

 peptones, delays the final digestion of proteins and eventually 

 suspends it. If the mixture be then diluted with water, digestion 

 is resumed. If the peptones are removed by diffusion through a 

 dialyser as fast as they are formed, so that the original concentra- 

 tion of pepsin and acid is maintained, the mixture recovers its 

 initial digestive force. This must occur during natural digestion 

 in the stomach, because the peptones are absorbed as fast as they 

 are formed. In fact, only a mere trace of them can be found in 

 the contents of the stomach during the digestion of protein. 

 Briicke, on the strength of this, assumes that pepsin undergoes no 

 change during its digestive action. Griitzuer's latest results, 

 however, make it probable that a little of the pepsin is consumed, 

 or loses its enzymatic properties (possibly by combining with other 

 colloidal substances), because even under the most favourable 

 circumstances the digestive power of any juice declines slowly. 



('/) The addition of concentrated alkalies or acids destroys 

 the digestive action of pepsin, as does heating to 70 C. Bile, too, 

 suspends the action of gastric digestion in vitro, even in such a 

 small quantity that the acidity of the juice is not neutralised. 

 This seems, however, not to occur during natural gastric 

 digestion, since Oddi noted no digestive disorders in dogs in 

 which the gall-bladder had been put in communication with the 

 abdominal cavity by a fistula. It is probable that the bile poured 

 into the stomach under these conditions is rapidly absorbed 

 again without admixture with the gastric contents. Or it may 

 be assumed that the absence of digestive disturbance is due to 

 the fact that in dogs the suspension of the gastric function is not 

 of much importance, since it is readily compensated by a more 

 active duodenal digestion. 



(e) The peptonisation of proteins by the gastric juice is not 

 immediate, but takes place in stages, several intermediate substances 

 being formed before reaching the end-substances represented by 

 the peptones by a process analogous to the action of saliva on 

 starch. These modifications of protein by the gastric juice can 

 only be demonstrated by prolonged artificial digestion. After 

 some hours of digestion in vitro (at 35-45 C.) of a given quantity 

 of boiled fibrin (or cubes of coagulated egg-albumin) in a very 

 active, artificial gastric juice, at least three different kinds of 

 proteins can be detected in the mixture : an acid albumin or 



