186 PHYSIOLOGY. 



direction in which the motion was begun. But as the force 

 here is gentle, and as, in the long course of the canal, there oc- 

 cur many flexures, different positions, and occasional irrita- 

 tions, it is obvious that resistances and stronger contractions 

 may frequently occur here, to change the direction of the mo- 

 tion ; accordingly we find it frequently changed, and directed 

 from below upwards, in so far that the contents of the intestines 

 frequently pass into the stomach. But the motions of the in- 

 testines are, however, most constantly directed from above 

 downwards, both because they are commonly begun from the 

 stomach, and because, when inversions do occur, there is com- 

 monly still so much resistance at the pylorus, and more espe- 

 cially at the valve of the colon, as to turn the direction again 

 into its proper course. In the colon, from its position, struc- 

 ture, and the consistence of its contents, the progress of these 

 is more slow and difficult, and it is therefore here assisted by 

 the longitudinal fibres peculiarly disposed, so as by their con- 

 traction to contribute more to the dilatation of every succeed- 

 ing portion of the intestine. 



CCXXVI. The chyle is taken into the lacteals, and moved 

 onwards in these in the same manner (CLXVII.) as the lymph 

 is in the several lymphatics in other parts of the body, to which 

 the lacteals are in structure and situation exactly similar. 



CCXXVI I. The course of the alimentary matters, and the 

 motions by which they are carried on, being now explained, we 

 return to consider the several changes which the aliment under- 

 goes in this course. 



CCXXVIII. In the mouth, if the aliment taken in be of a 

 solid consistence, it is here, as we have said, subjected to a tri- 

 ture ; and if our food is of a soft and moist kind, we are in- 

 stinctively directed to take in along with it some dry matter, as 

 bread, that the whole may be subjected more certainly to a 

 complete manducation. By this our aliment is not only more 

 minutely broken down, but is also intimately mixed with the 

 liquids at the same time taken in, with the saliva and other 

 fluids of the mouth, and with a quantity of air entangled by 

 these viscid fluids. 



CCXXIX, In this divided and moistened state, the aliment 

 is taken down into the stomach, where it is farther dissolved ; 



