NECESSITY FOR CHANGES OF DIET. 207 



the relative quantities of the necessary elements which they 

 contain. 



In actual practice, moreover, the quantity and kind of food 

 to be taken with most economy and advantage cannot be set- 

 tled for each individual, only by considerations of the exact 

 quantities of certain elements that are required. Much will 

 of necessity depend on the habits and digestive powers of the 

 individual, on the state of his excretory organs, and on many 

 other circumstances. Food which to one person is appropriate 

 enough, may be quite unfit for another ; and the changes of 

 diet so instinctively practiced by all to whom they are possi- 

 ble, have much more reliable grounds of justification than any 

 which could be framed on theoretical considerations only. 



In many of the experiments on the digestibility of various 

 articles of food, disgust at the sameness of the diet may have 

 had as much to do with inability to consume and digest it, as 

 the want of nutritious properties in the substances which were 

 experimented on. And that disease may occur from the want 

 of particular food, is well shown by the occurrence of scurvy 

 when fresh vegetables are deficient, and its rapid cure when 

 they are again eaten : and the disease which is here so re- 

 markably evident in its symptoms, causes, and cure, is matched 

 by numberless other ailments, the causes of which, however, 

 although analogous, are less exactly known, and therefore less 

 easily combated. 



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 per- 

 formed, that the quantity of food necessary for a healthy man, 

 taking free exercise in the open air, is as follows : 



Meat, . . . .16 ounces, or 1.00 Ib. avoird. 



Bread, . " . . .19 " 1.19 " " 



Butter or Fat, . 3J " 0.22 " " 



Water,. . . . 52 fluid oz. 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 circum- 

 stances 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 03sophagus into the stomach, and from this into the small 



