ii EXTERNAL DIGESTIVE SECRETIONS 127 



and afterwards Vella, stated that it had the property of digesting 

 all proteins, which (if true) would raise the physiological value of 

 succus entericus to that of pancreatic secretion. The best work 

 with artificial digestions of succus entericus and boiled egg- 

 white, flesh, and proteins in general (putrefaction being avoided), 

 has, however, given entirely negative effects (Thiry, Wenz, Boccardi, 

 Malerba and Jappelli, Bastianelli, Klug, Pregl, and others). 



But if succus entericus is incapable of digesting coagulated 

 albumin and natural proteins, it does contain a special enzyme, 

 Cohnheim's erepsin (1902), which acts on peptones, and splits 

 them into their final crystallisable products. All authors do not 

 agree in giving erepsin the importance which Cohnheim attributes 

 to it. Kutscher maintains that tryptic digestion alone is capable 

 of completely splitting the proteins until the biuret reaction 

 disappears. Bottazzi experimenting with intestinal extract 

 denies, on the strength of his results, that this particular pro- 

 teolytic enzyme is secreted by the intestinal mucosa. He refers it 

 to the activity of the trypsin secreted by the pancreas, and left to 

 a greater or less extent adherent to the intestinal mucosa. We 

 shall return to this in discussing intestinal digestion. 



The existence of a lipolytic enzyme (or lipase) in succus 

 entericus was long a subject of discussion. Early experimenters 

 (Vella, Schiff) were inclined to admit its presence ; but later work 

 with the natural secretion, given necessary precautions for pre- 

 venting putrefaction (Malerba, Jappelli, Bastianelli, Pregl, and 

 others), proved that there was no true lipolytic action, or that 

 it could only be minimal. Thus Lombroso, on investigating 

 the succus entericus secreted naturally by a loop of Vella during 

 digestion, or after injections of pilocarpine, observed that it had 

 a very slight lipolytic activity. He found, however, that the 

 intestinal secretion poured out in large quantities when a higher 

 fatty acid is introduced into the loop, is actively lipolytic to an 

 extent approximating to that of the pancreatic secretion. 



But the lipolytic enzyme of intestinal, unlike that of pancreatic, 

 juice is not aided in its action by bile. Lombroso's observation 

 cannot be met by the objection made to earlier workers, viz. that 

 the positive result is due to the presence of pancreatic enzymes 

 in the mucous membrane of the intestine, for the succus 

 entericus exhibiting this lipolytic activity is excited only by 

 definite stimuli (fatty acids), and does not diminish even when, 

 by repeated experiment, many hundred c.c. of juice have been 

 secreted by the Vella's loop. 



Besides these enzymes, which are normally contained in the 

 mucous coat of the intestine, there is in mammals during the 

 secreting period an enzyme (lactase) capable of transforming 

 lactose (which is not directly utilisable by the body) into glucose 

 and galactose (Beyerick, Fischer and Niebel, Portier, Orban). 



