284 THE TISSUES AND MECHANISMS OF DIGESTION. 



time. We infer that the proteid molecules are in some way built up out of 

 " fatty acid " and " aromatic " molecules, together with other components, 

 and we shall later on see additional reasons for this view. 



Among the supplementary products of pancreatic digestion may be men- 

 tioned the body indol (C 8 H 7 N), to which apparently the strong and pecu- 

 liarly fecal odor which sometimes makes its appearance during pancreatic 

 digestion is due. Indol, however, unlike the leucin and tyrosin, is not a 

 product of pure pancreatic digestion, but of an accompanying decomposition 

 due to the action of organized ferments. A pancreatic digestive mixture 

 soon becomes swarming with bacteria, in spite of ordinary precautions, when 

 natural juice or an infusion of the gland is used. When isolated ferment 

 is used and atmospheric germs are excluded, or when pancreatic digestion 

 is carried on in the presence of salicylic acid or thymol, which prevent the 

 development of bacteria and like organisms but permit the action of the 

 trypsin, no odor is perceived and no indol is produced. 



After long-continued digestion, especially when accompanied by putre- 

 factive decomposition, the amount of proteids which are carried beyond the 

 peptone stage and broken up may be very great. 



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 con- 

 nective tissue are not digested by pancreatic juice, which in this respect 

 affords a striking contrast to gastric juice. But when they have been pre- 

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

 gelatin, 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 toward nuclein, horny tissues, and the so-called 

 amyloid matter. 



On fats pancreatic juice has a twofold action. In the first place it emul- 

 sifies 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 last- 

 ing 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 shows that the 

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

 gland has similar emulsifying powers. In the second place pancreatic juice 

 splits up neutral fats into their respective acids and glycerin. Thus, palmitin 

 (or tripalmitin) (C 15 H 31 .CO.O) 3 .C3H5 is with the assumption of 3H 2 O split up 

 into three molecules of palmitic acid 3(Ci 5 H 31 .CO.OH) and one of glycerin 

 (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 appro- 

 priate means not only the corresponding fatty acids, but glycerin may be 

 obtained from the mixture. When alkali is present, the fatty acids thus set 

 free form their corresponding soaps. Pancreatic juice contains fat and is 

 consequently apt after collection to have its alkalinity reduced, and an 

 aqueous infusion of a pancreatic gland (which always contains a consider- 

 able 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 depend- 



