CHAP, i.] DIGESTION. 297 



ligaturing the bile-ducts, and leading all the bile externally through 

 a fistula of the gall bladder, is open to .objection, since it so 

 exhausts the animal as indirectly to affect digestion, still the 

 results of Bidder and Schmidt, in which the resorption of fat was 

 distinctly lessened (the quantity of fat in the lacteals falling from 

 3*2 to *02 p.c.) by the ligature and fistula, obviously point to the 

 same conclusion. That in man the succus entericus possesses a 

 wholly insufficient emulsifying power is shewn by the observation 

 of Busch, in a case where 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 pancreatic juice were but slightly 

 digested. Without denying the possible assistance of the succus 

 entericus, or even of gastric juice, we may conclude that the diges- 

 tion of fat is in the main carried out by the conjoint action of bile 

 and pancreatic juice. 



We have seen that the addition of bile to a digesting mixture 

 gives rise to a precipitate consisting of parapeptone, and bile salts 

 with some pepsin, but that on the further addition of bile this pre- 

 cipitate is redissolved. In the upper part of the duodenum the 

 inner surface, if examined while digestion is going on, is found to be 

 lined by a coloured granular material, which is probably a precipi- 

 tate thus formed ; but the purpose of its formation does not seem 

 . clear. It is more important to remember that not only is bile anta- 

 gonistic to peptic digestion, but apparently pepsin is destroyed by 

 trypsin in an alkaline medium, so that with the flow of bile and 

 pancreatic juice into the duodenum the processes 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 de- 

 stroys the active constituents of saliva, and of pancreatic juice (pro- 

 bably also those of the succus entericus), it is in its turn antagonized 

 or destroyed by the bile and the other alkaline juices of the intes- 

 tine. Hence pancreatic juice introduced 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. To what 

 stage the pancreatic digestion is carried, whether peptone is chiefly 

 formed, and when formed at once absorbed, or whether the pan- 

 creatic juice in the body, as out of the body, carries on its work 

 in the more destructive form, whereby the proteid material sub- 

 jected to it is broken dawn largely into leucin and tyrosin, is 



