272 OF FOOD AND THE DIGESTIVE PROCESS. 



insufficiency in the supply of nutriment prepared for the absorbent 

 vessels. 



477. On the other hand, that one great object of the secretion is to 

 withdraw from the Blood certain products of the decomposition of the 

 tissues, which would otherwise accumulate in it, and would be deleterious 

 to its character, is shown by evidence yet more decisive. We find that 

 the action of the Liver is constant, and not occasional, like that of the 

 Salivary and Gastric glands ; and that, if anything interfere with the 

 secreting process, and thereby cause the accumulation of the elements 

 of the bile in the blood, the effects of their presence are immediately 

 manifested in the disorder of other functions, especially those of the 

 nervous system ( 399) ; and the continued suspension of the function 

 leads to a fatal result, unless the elements of the bile are drawn off (as 

 sometimes happens) by the urinary organs. When the secreting action 

 of the liver has once been performed, an obstruction to the discharge of 

 the bile into the intestine does not seem to be so immediately injurious. 

 The fluid accumulates, and distends the bile-ducts and the gall-bladder ; 

 and when they are completely filled, part of it is reabsorbed into the 

 blood, apparently in a changed condition, since it does not then produce 

 the same injurious effects, as result from the accumulation of the same 

 materials, previously to the action of the Liver upon them. The colour- 

 ing matter seems to be very readily taken back into the circulating 

 system ; and is deposited by it in almost every tissue of the body. 



478. Although the secreting action of the Liver is constant, yet the 

 discharge of bile into the intestine is certainly favoured by the presence 

 of chyme in the latter. The purpose of the gall-bladder is obviously to 

 permit the accumulation of bile, when it is not wanted in the intestine ; 

 and we find it most constantly present in those tribes of animals, which 

 live upon animal food, and which therefore take their aliment at inter- 

 vals ; whilst it is more frequently absent in those herbivorous animals, 

 in which the digestive process is almost constantly going on. The 

 middle coat of the bile-ducts is clearly muscular, and has a peristaltic 

 action like that of the intestinal canal ; this action may be excited by 

 galvanism, or by irritation of the branches of the Sympathetic nerve, 

 by which it is supplied. The mucous coat of the ductus choledochus is 

 disposed in valvular folds, in such a manner as to prevent the reflux of 

 the bile or of the contents of the intestine ; and a still further security 

 is afforded by the valvular covering to the orifice of the duct, which is 

 furnished by the mucous covering of the intestine itself. The flow of 

 bile into the intestine, when its presence is needed there, is commonly 

 imputed to the pressure of the distended Duodenum against the gall- 

 bladder ; but it is probable that the contractility of the muscular coat 

 of the duct itself, which may be excited either through the sympathetic 

 nerve, or by irritation at the orifice of the duct (as in the case of the 

 Salivary glands), is the real cause of the discharge of the fluid. It is 

 an interesting fact, which proves how much the passage of the Bile into 

 the Intestine is dependent upon the presence of aliment in the latter, 

 that the gall-bladder is almost invariably found turgid in persons who 

 have died of starvation ; the secretion having accumulated, through the 

 want of demand for it, although there was no obstacle to its exit. 



