PAXCKEATIC DIGESTION 63- 



of hydrolysis to split the heavy proteid molecule into smaller and 

 smaller molecides ; first we get proteoses, then peptones, and finally 

 simple substances like leucine and tj-rosine : the formation of 

 leucine, tyrosine, &c., does not occur to any great extent in normal 

 digestion, for these simple materials are of little or no nutritive value. 

 The substance formerly called antipeptone is really not a peptone at 

 all. Siegfried showed it is a substance of low molecular weight, and 

 according to him it is identical with a substance he bad previously 

 -jparated from muscle, and called camic acid (C10H15N3O5). 

 i urther work by Kutscher has shown that Siegfiied is probably 

 wrong in regarding antipeptone as a single substance, but that it is in 

 reality a mixture of several substances of which he has separated out 

 he hexone bases arginine and histidine (see p. 32) and aspartic acid. 

 At any rate antipeptone is not on the same level as the true peptones, 

 which are capable of utilisation by the organism, but is in the same 

 category as leucine and tyrosine and similar materials of low mole- 

 cular weight. 



These facts can all be easily accounted for on the supposition that 

 a variable fraction of the proteid molecule is broken off virith com- 

 parative ease, and appears as leucine, tyrosine, and other amido-acids. 

 This is more easily performed by the more powerful trj-ptic enzyme 

 than by the comparatively feeble agent pepsin. Pepsin, however, 

 is not entirely inactive in this direction, for although leucine and 

 tjTosine cannot as a rule be found in a gastric digestion, yet there 

 are analogous substances of low molecular weight (aspartic acid and 

 the hexone bases) which were incorrectly grouped together by the 

 earlier workers as a peptone (antipeptone). 



2. Action of Amylopsin. — The conversion of starch into maltose 

 is the most powerful and rapid of all the actions of the pancreatic 

 juice. It is much more powerful than saliva, and will act even on 

 unboiled starch. The absence of this ferment in the pancreatic juice 

 of infants is an indication that milk, and not starch, is their natural 

 diet. 



3. Action on Fats. — The action of pancreatic juice on fats is a 

 double one : it forms an emulsion, and it decomposes the fats into 

 fatty acids and glycerin by means of its fat-spUtting ferment steapsin. 

 The fatty acids unite with the alkaline bases to form soaps {saponifica- 

 tion). The chemistry of this is described on p. 18. The fat-spHtting 

 power of pancreatic juice cannot be studied with a glycerin extract, 

 as steapsin is not soluble in glycerin : either the fresh juice or a 

 ■watery extract of pancreas must be used. 



The formation of an emulsion may be studied in this way. Shake 



