

CHYLIFICATION. 37 



These excretory canals unite so as to form smaller and 

 larger trunks successively, until they terminate in a single 

 trunk, which, after a certain course, terminates in the duo- 

 denum a short way from the pyloric orifice of the stomach. 

 The hepatic tube thus described communicates by a short 

 tube with the gall-bladder, which is maintained full of bile 

 by means of the cystic duct. 



In the lower animals the liver is often replaced by an ag- 

 glomeration of small tubes terminating in cul de sacs, and 

 inserted by their open mouths into the branches of an excre- 

 tory canal (as in the crabs and lobsters), or by simple but 

 long vessels, as in insects. Finally, in beings of a very simple 

 organization, the liver is either wanting or replaced by a glan- 

 dular tissue surrounding a portion of the intestine ; neverthe- 

 less, it is one of the organs found most constantly to exist in 

 the animal kingdom. 



69. The bile is a viscous liquid, greenish in colour, 

 thready, and extremely bitter. It is always alkaline, and has 

 a strong analogy with soap. 



Chemical analysis shows it to be composed of a salt formed 

 of soda united to a fatty acid of a peculiar nature, cholesterine, 

 a colouring principle, a little of the oleate or margarate of 

 soda, mucus, and water. But the bile has other uses, fur- 

 nishing peculiar substances to the blood. 



70. The pancreatic juice strongly resembles saliva, 

 physically and chemically ; but, in addition, it rapidly unites 

 into an emulsion with fatty bodies ; the pancreatic gland,* 

 which forms it, resembles the salivary glands in structure, 

 In man it is a granular mass, divided into a great num- 

 ber of lobes and lobules, firm in consistence, and of a greyish 

 colour, slightly reddish, situated transversely between the 

 stomach and vertebral column (Fig. 24). From each of the 

 granulations there arises a fine duct, and all these reunite to 

 form a canal which opens into the duodenum close to the 

 entrance of the bile duct. 



71. Formation of the Chyle. The chyme formed in the 

 stomach enters the intestine by the pyloric orifice of this 

 viscus, and passes through the intestine by its peristaltic 

 motion. During this passage it mingles with the bile, pan- 

 creatic juice, and other secretions from the mucous mem- 

 brane of the intestine, and gradually changes its properties ; 



* From TTO.V all, and Kpe'as, flesh. 



