310 THE TISSUES AND MECHANISMS OF DIGESTION. 



juice was necessary for the digestion and absorption of fatty food. That the 

 pancreatic juice does produce in the intestine such a change as favors the 

 transference of neutral fats from the intestine into the lacteals is shown by 

 the fact that in diseases affecting the pancreas much fatty food frequently 

 passes through the intestine undigested and great wasting ensues ; but it 

 cannot be maintained that the pancreatic juice is the sole agent in this 

 matter, since in animals in which the pancreatic ducts have been success- 

 fully ligatured chyle is still found in the lacteals. On the other hand, that 

 the bile is of use in the digestion of fat is shown by the prevalence of fatty 

 stools in case of obstruction of the bile-ducts ; and though the operation of 

 ligaturing the bile-ducts and leading all the bile externally through a fistula 

 of the gall-bladder is open to objection, since it in some way or other so 

 exhausts the animal as indirectly to affect digestion, still the results of experi- 

 ments in which the resorption of fat was distinctly lessened (the quantity of 

 fat in the lacteals falling from 3.2 to 0.2 per cent.) by the ligature and fistula 

 obviously point to the same conclusion. That in man the succus entericus 

 possesses a wholly insufficient emulsifying power is shown by the observa- 

 tion of a case in which the duodenum opened on the surface by a fistula 

 in such a way that the lower part of the intestine could be kept free from 

 the contents of the upper part containing the bile and pancreatic juice 

 and matters proceeding from the stomach. Fats introduced into the lower 

 part, where they could not be acted upon either by the bile or by the pan- 

 creatic juice, were but slightly digested. Without denying the possible 

 assistance of the succus entericus, or even of gastric juice, we may con- 

 clude that the digestion of fat is in the main carried out by the conjoint 

 action of bile and pancreatic juice. 



242. We have seen ( 216) that the addition of bile to a digesting 

 mixture gives rise to a precipitate. This is partly a coarse, flocculent pre- 

 cipitate, consisting of parapeptone with some amount of bile acids, and 

 partly of a finer, more granular precipitate, which is longer in falling down 

 and consists chiefly of bile acids with a variable amount of peptone ; the 

 latter is redissolved on the further addition of bile, even though the reaction 

 of the mixture remain acid. In the upper part of the duodenum the inner 

 surface, if examined while digestion is going on, is found to be lined by a 

 colored flocculent and granular material, which is probably a precipitate 

 thus formed ; the purpose of this precipitation is probably to delay the 

 passage of the undigested parapeptone along the duodenum. Moreover, 

 apart from this precipitation, bile arrests the action of pepsin, even while 

 the reaction of the mixture still remains acid ; and as soon as an alkaline 

 reaction is established the pepsin is apparently destroyed by the trypsin, so 

 that with the flow of bile and pancreatic juice into the duodenum the pro- 

 cesses which have been going on in the stomach come to an end. In fact, it 

 would seem that the juices of the various districts of the alimentary canal 

 are mutually destructive ; thus, while pepsin in an acid solution destroys the 

 active constituents of saliva and of pancreatic juice (probably also those of 

 the succus entericus), it is in its turn antagonized or destroyed by the bile 

 and the other alkaline juices of the intestine. Hence, pancreatic juice intro- 

 duced through the mouth must lose its powers in the stomach, and can only 

 be of use as an alkaline medium containing certain proteid matters. On 

 the other hand, if, as we have reason to believe, the contents of the stomach 

 as they issue from the pylorus still contain a large quantity of undigested 

 proteids, these must be digested by the pancreatic juice (with or without the 

 assistance of the succus entericus), the action of which seems to be assisted, 

 or at least not hindered, by bile. And in dogs fed through a duodenal fis- 

 tula, so that all gastric digestion is excluded, proteids are completely digested 



