DIGESTION 191 



of the broad inner zone began to pass toward the lumen of the acinus and to 

 disappear gradually as the secretion was poured out, while the outer zone 

 increased in width until almost the entire cell became clear and homogeneous. 

 (See Fig. 79.) After secretion ceased the granules again made their appear- 

 ance, the result, in all probability, of metabolic activity. 



Physiologic Action of Pancreatic Juice. Experimental investi- 

 gations have demonstrated the fact that pancreatic juice is the most complex 

 in its physiologic action of all the digestive fluids. By virtue of its contained 

 enzymes, pancreatic juice acts: 



1. On starch. When normal pancreatic juice or a glycerin extract of 

 the gland is added to a solution of hydrated starch, the latter is speedily 

 transformed into maltose, passing through the intermediate stage of dextrin. 

 The process is in all respects similar to that observed in the digestion of 

 starch by saliva. Pancreatic juice, however, is more energetic in this respect 

 than saliva. The enzyme which effects this change is termed amyhpsm. 

 When the starch which escapes salivary digestion passes into the small 

 intestine and mingles with pancreatic juice, it is very promptly converted into 

 maltose by the action or in the presence of this enzyme. 



2 . On Protein . It is stated that when protein is subjected to the action 

 of pure pancreatic juice it undergoes no digestive transformation for the 

 reason that the necessary enzyme has not as yet been developed; but after 

 the discharge of the juice into the intestine and after it comes into con- 

 tact with the duodenal mucous membrane or when it is mixed with in- 

 testinal juice it acquires marked proteolytic activity. It is therefore 

 generally believed that the pancreatic juice at the moment of its discharge 

 does not contain the proteolytic enzyme (trypsin) but only its precursor 

 (trypsinogen) ; that only when the latter comes into relation with the in- 

 testinal juice is the former developed. This has been attributed to action 

 of a special activating agent, secreted by the intestinal epithelium to 

 which the term, entero-kinase 1 has been given by Pavlov. Nevertheless 

 when protein compounds are subjected to the action of artificial pancreatic 

 juice, they are transformed into peptones which do not differ in essential 

 respects from those formed by the action of gastric juice. The inter- 

 mediate stages, however, are believed to be somewhat different. 



When fibrin, for example, is added to an extract of the pancreas in a 

 solution rendered alkaline by sodium carbonate, it becomes corroded on 

 the surface, fragile, and in a short time undergoes solution. The first 

 product is a compound termed alkali-protein. After solution has taken 

 place, various chemic changes are initiated which eventuate in the pro- 

 duction of peptone. The intermediate stages in this process have not 

 been satisfactorily determined. At no .time during artificial pancreatic 

 digestion is there any evidence of the presence of the primary' proteoses. 

 The secondary proteoses, however, are usually present. If an artificial 

 pancreatic juice or an extract of the pancreas can thus digest proteins then 

 trypsin, or some similarly acting enzyme, must be developed in the gland 

 during its preparation. 



1 An activator may be defined as an agent, which secreted by some one organ, is capable of 

 converting an inactive agent, secreted by some correlated organ, near or remote, into an active 

 agent by some chemical interaction. Thus the antecedents of many enzymes, either before or 

 after their discharge by gland cells are inactive and require to be modified in some unknown way 

 before they become functionally active. The term activator is usually applied to inorganic 

 agents, the term kinase to organic agents. 



