CHAP, i.] TISSUES AND MECHANISMS OF DIGESTION. 501 



of the soaps which are formed. Now the bile and pancreatic 

 juice supply just such conditions as the above for emulsionis- 

 ing fats : they both together afford an alkaline medium, the 

 pancreatic juice gives rise to an adequate amount of free fatty 

 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. The fat of 

 milk, being already in a condition of emulsion, does not so much 

 need the help of these juices. 



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 

 digestion and absorption of fatty food. That the pancreatic juice 

 does produce in the intestine such a change as favours the trans- 

 ference 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 assistance of 

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



