THE JEJUNUM AND ILIUM. 331 



of the heart, where it is mixed with the venous blood returned from 

 every part. By the power of the heart it is propelled through the 

 lungs, where it is purified and vitalized : and having been returned 

 to this organ it is driven through other vessels all over the frame, 

 and bestows nutriment and life on every part. 



The food, in a state of perfect solution, and under the name of 

 chyme, is forced on by the muscular coat of the fourth stomach into 

 the duodenum, where another change immediately commences. The 

 food is separated into two distinct portions or principles — that 

 which is nutritive or capable of being imbibed by the lacteals — a 

 white fluid called chyle — and that which is either innutritive, or 

 which they reject, and which is propelled along the intestines and 

 finally evacuated. 



There has been much dispute as to the manner in which this 

 separation is effected. The chyme that has been formed by the 

 agency of the gastric juice may contain in itself a tendency to this 

 separation, or precipitation of the excrementitious part ; or this may 

 be effected by some fluid secreted from the mucous coat of the du- 

 odenum ; or the bile and the pancreatic juice may be the main 

 agents in producing the change. 



Ten or twelve inches down the duodenum, as may be seen at A, 

 p. 291, two ducts penetrate the coats of that intestine, and pour 

 into it the fluid secreted by the pancreas and liver. It would seem 

 likely, from the distance from the stomach at which these fluids 

 enter, that some change had already taken place in the contents of 

 the duodenum, which was to be perfected by means of these auxilia- 

 ries. The separation or precipitation is more rapidly and effectually 

 made ; while the bile also has some stimulating effect on the coats 

 of the stomach, urging the exhalents and the absorbents, and the 

 muscles of the intestines, to stronger and more effectual action ; and 

 the pancreatic juice may dilute the biliary secretion, and shield the 

 intestine from its occasional too great acrimony. 



While, however, the bile is thus acting in promoting healthy di- 

 gestion, (and no animals afford more frequent illustration of the con- 

 nection between the biliary secretion and the digestive process than 

 cattle do,) the true notion of it is perhaps, that it is an excremen- 

 titious substance, containing properties that would be noxious to the 

 constitution, but, as in most of the contrivances of nature, the mode 

 of its evacuation answers another and a salutary purpose. 



The duodenum terminates in the jejunum, but there is no assign- 

 able point where the one can be said to terminate and the other 

 begin. 



THE JEJUNUM AND ILEUM. 



These intestines, together with the^ duodenum, the caecum, and a 

 portion of the coloti, will be seen (in the cut p. 330, at Jigs. 2 and 3,) 



