520 DIGESTION IN THE INTESTINES [GIL XXXI V. 



even on unboiled starch. The absence of this enzyme in the pancreatic 

 juice of infants is an indication that rnilk, and not starch, is their 

 natural diet. 



3. Action on Pats. These are split by pancreatic lipase into 

 glycerin and fatty acids. The fatty acids unite with the alkaline 

 bases present to form soaps (saponification, see p. 415). If a glycerin 

 extract of pancreas is filtered, the filtrate has no lipoclastic action ; 

 the material deposited on the, filter is also inactive, but on mixing it 

 with the inactive filtrate once more, a strongly lipoclastic material is 

 obtained. In this way lipase is separable into two fractions: the 

 material on the filter is inactive lipase ; the material in the filtrate 

 is its co -enzyme ; the latter is not destroyed by boiling. Bile salts 

 also activate the inactive lipase, and this explains the fact that bile 

 favours fat-splitting. 



Pancreatic juice also assists in the emulsification of fats ; this it 

 is able to do because it is alkaline, and it is capable of liberat- 

 ing fatty acids, which form soaps with the alkali present; the 

 soap forming a film on the outer surface of each fat globule 

 prevents them running together. Emulsions are much more 

 permanent in the presence of such colloids as gum or protein. The 

 presence of protein in the pancreatic juice renders it therefore 

 specially suitable for the purpose of emulsification. 



4. Milk-curdling Enzyme. The addition of pancreatic extracts 

 or pancreatic juice to milk causes clotting ; but this action (which 

 differs in some particulars from the clotting caused by rennet) can 

 hardly ever be called into play, as the milk upon which the juice has 

 to act has been already curdled by the rennin of the stomach. 



The so-called Peripheral Reflex Secretion of the Pancreas. 



One of the most effective ways of producing a flow of pancreatic 

 juice is to introduce acid into the duodenum. Popielski and 

 Wertheimer and Le Page showed that this flow still occurs when the 

 nerves supplying the duodenum and pancreas have been cut through. 

 Wertheimer also mentions that the flow can be excited by injection 

 of acid into the jejunum, but not when it is injected into the lower 

 part of the ileum. These authors concluded that the secretion is a 

 local reflex, the centres being situated in the scattered ganglia of the 

 pancreas, or, in the case of the jejunum, in the ganglia of the solar 

 plexus. 



This subject has been reinvestigated by Starling and Bayliss, and 

 the results they have obtained are most noteworthy. They consider 

 that the secretion cannot be reflex, since it occurs after extirpation of 

 the solar plexus, and destruction of all nerves passing to an isolated 

 loop of intestine. Moreover, atropine does not paralyse the secretory 



