256 DIGESTION. 



With regard to the quantity, too, as well as the kind of 

 food necessary, there will be much diversity in different 

 individuals. Dr. Dalton believed, from some experiments 

 which he performed, that the quantity of food necessary 

 for a healthy man, taking free exercise in the open air, is 

 as follows: 



Meat .... 1 6 ounces, or I'oolb. avoird. 



Bread . . . . 19 ,, ,, 1-19 ,, 



Butter or Fat. . 3^ ,, ,, 0*22,, ,, 



Water . ... 52 fluid ozs. 3-38 ,, 



The quantity of meat, however, here given, is probably 

 more in proportion to the other articles of diet enumerated 

 than is needful for the majority of individuals under the 

 circumstances stated. 



PASSAGE OF FOOD THROUGH THE ALIMENTARY CANAL. 



The course of the food through the alimentary canal of 

 man will be readily seen from the accompanying diagram 

 (fig. 66). The food taken into the mouth passes thence 

 through the oesophagus into the stomach, and from this 

 into the small and large intestine successively; gradually 

 losing, by absorption, the greater portion of its nutritive 

 constituents. The residue, together with such matters as 

 may have been added to it in its passage, is discharged 

 from the rectum through the anus. 



We shall now consider, in detail, the process of diges- 

 tion, as it takes place in each stage of this journey of the 

 food through the alimentary canal. 



The Salivary Glands and the Saliva.. 



The first of a series of changes to which the food is sub- 

 jected in the digestive canal, takes place in the cavity of 

 the mouth ; the solid articles of food are here submitted to 

 the action of the teeth (p. 59), whereby they are divided 



