THE SPLEEN; 297 



nutritive portion of the food from chyme into chyle, and separating it from that 

 which, containing little or no nutriment, is voided as excrement. 



Almost every part of it is closely invested hy the peritoneum, which seems 

 to discharge the office of a capsule to this viscus. Its arteries are very small, 

 considering the bulk of the liver ; but their place is curiously supplied by a 

 vein — the vena porta — a vessel formed by the union of the splenic and 

 mesenteric veins, and which seems, if it does not quite usurp the office and 

 discharge the duty of the artery, to be far more concerned than it in the secre- 

 tion of the bile. There is a free intercourse between the vessels of the two. 



There are, scattered through the substance of the liver, numerous little gra- 

 nules, called acini, from their resemblance to the small stones of certain berries. 

 They are united together by a fine cellular web, whose intimate structure has 

 never yet been satisfactorily explained. From the blood which enters the liver 

 there is a constant secretion of a yellow bitter fluid, called bile. The separation 

 of the bile from the blood probably takes place within the acini ; the secreting 

 vessels are the penicelli, or those which compose this fine cellular web, and the 

 fluid — the bile — is taken up by the pori biliarii, small vessels, from which a 

 yellowish fluid is seen exuding into whatever part of the liver we cut, and is 

 carried by them into the main vessel, the hepatic duct. 



The bile, thus formed, is in most animals received into a reservoir, the gall- 

 bladder, whence it is conveyed into the duodenum (j), p. 286) at the times, 

 and in the quantities, which the purposes of digestion require ; but the horse 

 has no gall-bladder, and, consequently, the bile flows into the intestine as rapidly 

 as it is separated from the blood. The reason of this is plain. A small stomach 

 was given to the horse in order that the food might quickly pass out of it, and 

 the diaphragm and the lungs might not be injuriously pressed upon, when we 

 require his utmost spe&d ; and also that we might use him with little danger 

 compared with that which would attach to other animals, even when his stomach 

 is distended with food. Then the stomach, so small, and so speedily emptied, 

 must be oftener replenished ; the horse must be oftener eating, and food oftener 

 or almost continuously passing out of his stomach. How admirably does this 

 comport with the uninterrupted supply of bile !■ 



THE PANCREAS. 

 In the domestic animals which are used for food, this organ is called the sweet- 

 bread. It lies between the stomach and left kidney. It much resembles in 

 structure the salivary glands in the neighbourhood of the mouth, and the fluid 

 which it secretes has been erroneously supposed to resemble the saliva in its pro 

 perties. The pancreatic fluid is carried into the intestines by a duct which 

 enters at the same aperture with that from the liver. It contains a large pro- 

 portion of albumen, caseous matter, and a little free acid. Its use, whether to 

 dilute the bile or the chyme, or to assist in the separation of the chyme from 

 the feculent matter, has never been ascertained : it is, however, clearly employed 

 in aiding the process of digestion. 



THE SPLEEN. 

 This organ, often called the melt, is a long, bluish-brown substance, broad 

 and thick at one end, and tapering at the other j lying along the left side of the 

 stomach, and between it and the short ribs. It is of a spongy nature, divided 

 into numerous little cells not unlike a honeycomb, and over which thousands 

 of minute vessels thickly spread. The particular use of this organ has never 

 been clearly ascertained, for in some cruel experiments it has been removed 

 without apparent injury to digestion or any other function. It is, however, 

 useful, at least occasionally, or it would not have been given to the animal. It 



