CHAP. IX.] THE ENZYMES OF THE INTESTINAL JUICE. 



415 



who have experimented on this Subject that the mucous membrane 

 possesses a much more marked inverting action than the intestinal 

 juice itself, so that inversion is obtained much more readily and 

 perfectly if a solution of cane-sugar be allowed to sojourn for a short 

 time in the intestine and thereafter be digested in the incubator, or 

 if it be digested with a small piece of air-dried mucous membrane, 

 than if it be mixed with succus entericus and then placed in the 

 incubator. 



In harmony with our knowledge of other enzymes, we may 

 provisionally, and with considerable probability, assume that the 

 mucous membrane of the intestine contains a zymogen of the in- 

 verting ferment which is sparingly diffusible, and that this zymogen 

 is broken up with the liberation of the free ferment when the cells 

 which contain it are in contact with cane-sugar. Brown and Heron 

 have shewn that the inverting action is never complete. As soon as 

 about 25 / of cane-sugar has been inverted, the process comes to an 

 end. It must be remembered, however, that experiments performed 

 in vitro give us but an imperfect conception of what occurs in the 

 living body. We have experimental proof of the facility with which 

 sugars are absorbed by the small intestine, and it is probable that as 

 the absorption of invert-sugar will occur pari passu with its pro- 

 duction, the conditions are present for the complete inversion of any 

 cane-sugar existing in the intestine. 



In Rohmann's experiments, the intestinal juice, obtained from a 

 Vella-fistula situated in the upper half of the small intestine, 

 possessed much greater inverting power than that of two other 

 fistulse situated in the lower half. Brown and Heron, by digesting 

 weighed quantities of mucous membrane of pig's intestine with 3 per 

 cent, solutions of cane-sugar, at 40 C., found that the duodenum, 

 including Brunner's glands, possesses most feeble inverting power, no 

 inversion having occurred after digestion at this temperature during 

 a period of 3J hours. The jejunum and ileum possess very much 

 higher inverting activity and in about equal degree, except in the 

 situation of Peyer's patches, where the activity is at its highest. 



If we except man in a state of civilisation, cane-sugar can only 

 rarely find its way into the intestine, and it therefore appears strange 

 that an inverting ferment should be so widely distributed throughout 

 the intestinal mucous membrane. In all probability, however, the 

 inverting ferment which can resolve saccharose into dextrose and 

 levulose is the same ferment which possesses the power of splitting up 

 sugar of milk into dextrose and galactose. If this be the case we 

 have a ready explanation of its wide diffusion. 



The maltose- When malt-diastase acts upon a starch solution, the 



onverting en- SU g ar w hich results from its action is maltose. When 



the diastatic ferment of the pancreas acts upon starch, 



maltose is also formed, though subsequently a small fraction of this 



maltose is converted into grape sugar, according to Brown and Heron. 



