CHAP, i.] TISSUES AND MECHANISMS OF DIGESTION. 475 



acid, and the bile in addition brings into solution the soaps as they 

 are formed. So that we may speak of the emulsion of fats in the 

 small intestine as being carried on by the bile -and pancreatic juice 

 acting in conjunction ; and as a matter of fact the bile and pancreatic 

 juice do largely emulsify the contents of the small intestine, so that 

 the greyish turbid chyme is changed into a creamy-looking fluid, 

 which has been sometimes called chyle. It is advisable however 

 to reserve this name for the contents of the lacteals. Many of the 

 fats present in food, for instance, butter, already contain some fatty 

 acids when eaten ; for these fats the initial action of the pancreatic 

 juice is less necessary. 



This mutual help of bile and pancreatic juice in producing an 

 emulsion explains to a certain extent the controversy which long 

 existed between those who maintained that the bile and those who 

 maintained that the pancreatic juice was necessary for the diges- 

 tion and absorption of fatty food. That the pancreatic juice does 

 produce in the intestine such a change as favours the transference 

 of neutral fats from the intestine into the lacteals, is shewn 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 successfully ligatured chyle is still 

 found in the lacteals. On the other hand, that the bile is of use 

 in the digestion of fat is shewn by the prevalence of fatty stools 

 in cases 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 experiments 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 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 pancreatic juice 

 were but slightly digested. Without denying the possible assist- 

 ance of the succus entericus, or even of gastric juice, we may 

 conclude that the digestion of fat is in the main carried out by the 

 conjoint action of bile and pancreatic juice. 



281. We have seen, 247, that the addition of bile to a 

 digesting mixture gives rise to a precipitate. This is partly a 

 coarse flocculent precipitate, consisting of parapeptone with some 

 amount of bile acids, and partly of a finer more granular pre- 



