DIGESTION AND ABSORPTION. 101 



tubes, juices are poured out, called digestive juices, which 

 mix with the food, and make in it the very changes that 

 are required. These juices differ from each other, and 

 come into different portions of the canal. One juice acts 

 on one kind of food, and another juice on another kind. 



13. The butter and cream, and all the other fats, that we 

 eat, are acted on in a way peculiar to themselves. They 

 are not really made to dissolve in water; but a juice is 

 furnished, called the pancreatic juice, with which they 

 are so thoroughly mixed, that they will pass through that 

 part of the wall of the alimentary canal which is their 

 special way out. 



14. There are some other fluids, besides this pancreatic 

 juice, that oil will mix with; and such mixtures are called 

 emulsions. Milk is an emulsion. The oil-globules dif- 

 fused through it rise to the top, and make the cream ; and 

 from the cream we make butter, by the method already 

 described (Chap. VI, Sect. I., 23). We eat the butter. It 

 passes down, without being changed, until it reaches the 

 place where the pancreatic juice comes in. With that it 

 mixes; and all these little oil-globules are separated 

 again, and diffused through the fluid, just as they were at 

 first in the milk. This fluid is the chyle; and it looks 

 so very like milk, that the little hair-like tubes that carry 

 it away, after it has passed through the wall of the canal, 

 are called lacteals, or milk-vessels. (Latin, lac, milk.) 



15. The muscle in the walls of the canal has a good deal 

 to do with digestion, as well as the juices inside. It acts 

 in two ways : it forces the food along, and it kneads and 

 mixes it with the juices. We know how the muscles of 

 the mouth and throat close about it, when we swallow. 

 These are voluntary muscles, and we are conscious of their 



