SECRETION OF BILE. 273 



479. The composition of the Bile, and the structure of the organ 

 which elaborates it, will be more appropriately considered hereafter, 

 when the Secreting apparatus generally is being described (CHAP, ix.) 

 At present we have to inquire what is the precise effect of its admixture 

 with the products of digestion, and what is the purpose which this ad- 

 mixture serves. In the first place, it may be stated that biliary matter 

 is essentially a soap, formed by the union of a fatty acid with a soda- 

 base ; and that it serves the purpose of neutralizing the acidity of the 

 chyme, which is derived from the gastric juice ; the biliary acids falling 

 down as an insoluble precipitate, when thus deprived of their soda. 

 Further, the bile shares with the pancreatic fluid in tnat emulsifying 

 power, by which the fatty matters of the food are reduced to a state of 

 such fine division, as to be rendered capable of being absorbed ; and 

 thus it happens that the introduction of these matters into the system, 

 through the medium of the lacteal absorbents (494), does not take 

 place until after the chynle has been mingled with the biliary and pan- 

 creatic secretions. Again, it has been asserted (but the fact has not 

 been fully substantiated), that the admixture of biliary matter produces 

 a conversion of saccharine into fatty compounds. When fresh bile is 

 mingled with newly-formed chyme, in a glass vessel, the mixture sepa- 

 rates into three distinct parts ; a reddish-brown sediment at the bottom, 

 a whey-coloured fluid in the centre, and a creamy pellicle at the top. 

 The central stratum probably contains the albuminous, gelatinous, sac- 

 charine, and other matters in a state of solution ; the superficial pellicle 

 may be looked upon as consisting chiefly of oleaginous matter destined 

 for absorption ; whilst the sediment, partly consisting of the unreducible 

 portion of the food, and partly of the biliary matter itself, is evidently 

 excrementitious. 



480. The Pancreatic secretion has a chemical constitution very ana- 

 logous to that of Saliva ; but the peculiar organic compound which it 

 contains, has been' found by M. Bernard to possess a power of emulsify- 

 ing fatty matter, when mingled with it ; and there is strong reason to 

 believe that the chief purpose of this secretion is to effect such a change 

 in the condition of the oleaginous constituents of the chyme, as may 

 prepare them for absorption. But further, the neutralization of the acid 

 of the gastric fluid now allows the metamorphosis of starch to be recom- 

 menced ; and as there is evidence that the production of sugar continues 

 to take place during the passage of the chymous mass along the small 

 intestines, in animals whose food is partly or completely vegetable, the 

 pancreatic fluid, which has been experimentally ascertained to possess 

 this power, is probably the chief agent by which the conversion is effected. 

 It may be surmised, further, that the glandulse of Brunner ( 450) par- 

 ticipate in the functions of the Pancreas ; being, perhaps, the chief 

 agents in the elimination of that "succus entericus," which has been 

 experimentally found to concur with the biliary and pancreatic fluids in 

 the emulsification of fatty matters. 



481. During the passage of the contents of the Intestine, now aug- 

 mented by the biliary secretion, along the canal, the nutritious portion 

 is gradually withdrawn by the absorbent vessels on its walls ; and the 

 excrementitious matter alone remains, increased in amount by the pro- 



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