240 * PHYSIOLOGY OF ALIMENTATION. 



A long-accepted explanation of the role of bile in hastening 

 fat digestion has been sought in its power of favoring the 

 emulsification of fats. Through emulsification of the fat the 

 amount of surface exposed to the action of lipase is greatly 

 increased. Experiments carried out by HEWLETT * indicate 

 that bile acts in yet another and even more direct way than 

 this in favoring the activity of the ferment. These experi- 

 ments show at the same time which constituent of the bile 

 it is that favors the fat-splitting activity of the pancreatic 

 juice, for bile is a mixture of a number of chemical entities. 



If, instead of the ordinary very sparingly soluble fats, the 

 soluble triacetin is used, so that the question of emulsification 

 plays no part whatsoever, it is found that bile still markedly 

 hastens the action of pancreatic juice upon this substance. 

 In one experiment, for example, pure pancreatic juice ob- 

 tained from a dog by secretin and atropin injections pro- 

 duced in one hour at 20 C. enough acid to require 0.5 c.c. 

 1/20 normal alkali solution to neutralize it, and in twenty- 

 four hours 12.6 c.c. In another tube which contained the 

 same amount of pancreatic juice and triacetin, but in addi- 

 tion a small amount of bile, the acidity produced in one hour 

 amounted to 13.0 c.c., in twenty-four hours to 18.6 c.c. of 

 a 1/20 normal alkali solution. That the acceleration of the 

 decomposition in the later hours of the experiment should 

 be less than in the earlier is readily explained by 'the fact 

 that the reaction is approaching an equilibrium. 



If now an attempt is made to discover which constituent 

 of the bile it is that favors in this way the decomposition of 

 triacetin under the influence of pancreatic juice, it is found, 

 first of all, that boiling the bile does not destroy this property. 

 It is therefore probable that we are not dealing with the 

 action of any enzyme contained in the bile. HEWLETT has 

 further shown that this property resides neither in the choles- 

 terin nor in the bile pigments, nor in variations in the reac- 



1 HEWLETT: Johns Hopkins Hospital Bulletin, 1905, XVI, p. 20. 



