CHAP, i.] TISSUES AND MECHANISMS OF DIGESTION. 429 



On the gelatiniferous elements of the tissues as they actually 

 exist in the tissue previous to any treatment pancreatic juice 

 appears to have no solvent action. The fibrillse and bundles of 

 fibrillse of ordinary untouched connective- tissue are not digested 

 by pancreatic juice, which in this respect affords a striking 

 contrast to gastric juice. But when they have been previously 

 treated with acid or boiled so as to become converted into actual 

 gelatine, trypsin is able to dissolve them, apparently changing 

 them much in the same way as does pepsin. Trypsin unlike 

 pepsin, will dissolve mucin. Like pepsin, it is inert towards 

 nuclein, horny tissues, and the so-called amyloid matter. 



On fats pancreatic juice has a twofold action. In the first 

 place it emulsifies fats. If hog's lard be gently heated until it 

 melts and be then mixed with pancreatic juice before it solidifies 

 on cooling, a creamy emulsion, lasting for almost an indefinite time, 

 is formed. So also when olive oil is shaken up with pancreatic 

 juice, the separation of the two fluids takes place very slowly, 

 and a drop of the mixture under the microscope shews that the 

 division of the fat is very minute. An alkaline aqueous infusion of 

 the gland has similar emulsifying powers. In the second place pan- 

 creatic juice splits up neutral fats into their respective acids and 

 glycerine. Thus palmitin (or tripalmitin) (C 15 H 31 . CO . 0) 3 . C 3 H 5 

 is with the assumption of 3H 2 split up into three molecules of 

 palmitic acid 3(C 15 H 31 .CO.OH) and one of glycerine (C 3 H 5 )(OH) 3 ; 

 and so with the other neutral fats. If perfectly neutral fat be 

 treated with pancreatic juice, especially at the body-temperature, 

 the emulsion which is formed speedily takes on an acid reaction, 

 and by appropriate means not only the corresponding fatty acids 

 but glycerine may be obtained from the mixture. When alkali 

 is present, the fatty acids thus set free form their corresponding 

 soaps. Pancreatic juice contains fats, and is consequently apt after 

 collection to have its alkalinity reduced ; and an aqueous infusion 

 of a pancreatic gland (which always contains a considerable amount 

 of fat) very speedily becomes acid. 



Thus pancreatic juice is remarkable for the power it possesses 

 of acting on all the food-stuffs, on starch, fats and proteids. 



The action on starch, the action on proteids, and the splitting 

 up of neutral fats appear to be due to the presence of three distinct 

 ferments, and methods have been suggested for isolating them. 

 The emulsifying power, on the other hand, is connected with the 

 general composition of the juice (or of the aqueous infusion of the 

 gland), being probably in large measure dependent on the alkali 

 and the alkali-albumin present. The proteolytic ferment trypsin 

 as ordinarily prepared seems to be proteid in nature and capable 

 of giving rise, by digestion, to peptone ; but it may be doubted, as 

 in the case of pepsin and other ferments, whether the pure ferment 

 has yet been isolated. There are no means of distinguishing the 

 amylolytic ferment of the pancreas from ptyalin. The term pan- 



