NTRODUCTION. 



51 



with blood-vessels, and secreting the gUstric jiffce — the principal 

 agent in digestion, and by means of which the. food is converted into 

 a uniform half fluid mass, called chyme. 



From the presence of this gastric juice, the fourth stomach .has the 

 property of curdling milk. The dried stomach or maw af calves is 

 called rennet. It will be seen, as we go on, that this property of 

 curdling milk is, in some states of the stomack or the milk, an occa- 

 sional source of disease. 



The food, being thus prepared, passes through the lower orifice of 

 the stomach into the intestines ; and these are of enormous length, in 

 order that every particle of nutriment may be extracted. They are 

 twenty-two times the length of the body of the ox. 



The food has not passed far into the first intestine ere it undergoes 

 a new change. The secretions from the liver and the pancreas — the 

 bile and the pancreatic juice — mingle with the food ; and at the same 

 time, and possibly influenced by these, the mass which has passed 

 the stomach begins to separate into two parts, the one a white matter, 

 constituting the nutritive portion, and called the chyle — the other, 

 that which is afterwards to be expelled from the system. The sepa- 

 ration is at first but partial : more and more nutritive matter is ex- 

 tracted as the mass rolls on, and, at length, nothing that is useful 

 remains. 



This nutritive matter, the chyle, is not suffered to pass far along 

 the intestinal can-al, but is taken up or absorbed by numerous minute 

 vessels that open on the inside of the bowels, and is conveyed by 

 them into the circulation, where it is mixed with the blood, and con- 

 verted into blood, and prepared for building up the various portions 

 of the frame. All along the small intestines, — the duodenum, jejunum, 

 and ileum, — this separation continues to be made, and these vessels 

 at length convey away all the useful portion of the food. 



The residue, having arrived at the larger intestines, which now 

 succeed, and containing no longer anything that can be thus changed 

 into chyle, these vessels, the lacteals, are no longer found in cattle; 

 but nevertheless there are other vessels, absorbents, which take up the 

 fluid parts of the faeces, and extract from them what may ultimately 

 contribute to nutriment. It is on this accoimt that, when an animal 

 is unable to eat, we can support him for a considerable period by 

 means of nutritive fluids injected into the bowels, and which can 

 only reach to the large intestines. 



In most herbiverous animals there is a provision made by a curious 

 cell-like structure of the colon and ccecum, (the most considerable of 

 the large intestines), for the retention of the residue of the food in 

 them ; but, in the ox and other ruminants, the food is so thoroughly 

 prepared by the complicated mechanism of the four stomachs, and 

 the course of the small intestines is so lengthened, that this structure 

 of the colon and coecum is not needed, and they are neither of extra- 

 ordinary size nor formed into cells. 



