INTRODUCTION. 25 



with blood-vessels, and secreting the g'astric juice — the principal 

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

 a uniforir half fluid mass, called chyme. 



From ^iie presence of this gastric juice, t'le fourth stomach has the 

 property of curdling milk. The dried sto -lach or maw of calves is 

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

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

 sional source of disease. 



The food, being thus prepared, passes tL^ough the lower orifice of 

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

 order that every particle of nutriment m?y 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 

 lime, and possibly influenced by these, the mass w'hich has passed 

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

 constituting the nutritive portion, and called the ch<jlc — the other, 

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

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

 tracted as the mass rolls on, and, at length, nGt,liihg that is useful 

 remains. 



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

 the intestinal canal, but is taken up or abso'.tved by numerous minute 

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

 them into the circulation, where it is miy.oi with the blood, and con- 

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

 of the frame. All along the small intestines, — the duodenum, j'sjunmn, 

 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 lacieals, 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 account 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 herbi --erous animals there is a provision made by a curious 

 cell-like structii -e of the colon and caecum, (the most consideral)>3 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 ccecum is not needed, and they are neither of extra- 

 ordinary size nor formed into cells 

 6 



