CLASS I. MAMMALIA. 23 



bag or sack, situated in the upper part of the abdomen, at 

 the spot usually called the pit of the stomach. It is capable 

 of great distention or contraction, according to the quantity 

 which is put into it. In the stomach, the food is acted on by 

 a peculiar fluid, called the gastric juice. It has no remarka- 

 ble sensible qualities, and is nearly tasteless and destitute of 

 odor ; but its operation upon the substances exposed to its 

 influence is very decided and powerful. They are gradually 

 reduced, of whatever kind they may be, to one homogeneous 

 mass, called chyme, of a grayish color, and of a consistence 

 like that of thick cream. This operation being completed, 

 the chym'e passes out of the stomach, by its lower or pyloric 

 orifice, situated towards the right side, into the intestines, 

 which form a long canal, and, taken together, are many times 

 ilonger than the body. j 



In the intestines, the chyme is subjected to the action of 

 ithe bile and pancreatic juice. The bile, or gall, is a brown- 

 icolored, viscid, and very bitter fluid, prepared by the liver, 

 i a large organ on the right side, just beneath the ribs, and col- 

 ilected into the gall-bladder, where a part of it is reserved for 

 use. The pancreatic juice resembles very nearly the saliva 

 iin color and appearance, and is prepared by the pancreas, 

 an organ situated just below the stomach. The effect of the 

 mixture of these two fluids with the chyme, is to separate it 

 into two parts. One of these is a thin, milky fluid, called 

 \chyle; the remainder consists of those portions of the food 

 jwhich are not fit for the nourishment of the system, but are 

 Irejected and thrown out of it, as useless. The chyle is grad- 

 iually absorbed by capillary vessels, called the lacteals, which 

 jopen into the intestines through nearly their whole course, 

 jand convey it into a vessel called the thoracic duct. This 

 jduct ascends from the abdomen along the back into the tho- 

 rax, and there empties its contents into the left subclavian 

 vein, the vein coming from the left arm, where the chyle is 

 I immediately mingled with the mass of blood, and enters with 

 iit into the circulation. The chyle is nearly the same, from 

 jwhatever substance it is prepared, when the digestion is per- 

 fect. Some kinds of food, however, are capable of furnish- 

 ting a larger proportion of it than others : this is the case with 

 animal food, of which it takes a smaller quantity to supply the 

 isystem with nourishment, than of vegetable. Animal sub- 

 stances are also more easy of digestion ; and hence, it is ob- 

 served, in those animals which subsist on vegetables, that the 

 i digestive organs are more various, extensive, and complicated, 



