446 THE POPULAR SCIENCE MONTHLY. 



pendently of the aid derived from our appetites, there is the great ad- 

 vantage of having foods which contain a proportion of nearly all these 

 elements ; and combinations of foods have been effected by experience 

 which protect even the most ignorant from evil consequences. 



Thus flesh, or the muscular tissue of animals, contains precisely the 

 elements which are required in our flesh-formers, and, only limited by 

 quantity, our heat-generators also ; and life may be maintained for 

 very lengthened periods upon that food and water when eaten in large 

 quantities. Seeing, moreover, that the source of flesh in animals which 

 are used as food is vegetables, it follows that vegetables should have 

 the same elements as flesh, and it is a fact of great interest that in 

 vegetables we have foods closely analogous to the flesh of animals. 

 Thus, in addition to water and salts, common to both, there is vegetable 

 jelly, vegetable albumen, vegetable fibrine, and vegetable caseine, all 

 having a composition almost identical with animal albumen, gelatine, 

 chondrine, and caseine. 



Hence our appetites and the bountiful provision made for us ex- 

 tend our choice to both the vegetable and animal kingdoms, and it is 

 possible to find vegetable foods on which man could live as long as 

 upon animal food alone. Bread is in vegetable foods that which flesh 

 is in animal foods, and each within itself contains nearly all the ele- 

 ments required for nutrition. 



When, however, we bring knowledge of a special kind to the aid 

 of our appetites, we are able to discover both the deficiencies in any 

 given food and the kind of food which would meet them. Thus a 

 knowledge of the requirements of the system and of the available 

 uses of food leads to the proper combinations of food, or to the con- 

 struction of dietaries. 



We have thus placed face to face the requirements of the body and 

 the qualities of the foods to be used to supply them, but it is of very 

 common observation that the effect of the supply is but temporary, 

 and needs renewal at definite periods. Hence we show that the needs 

 of the body are tolerably uniform, while the effect of the supply is 

 temporary, or that both the need and the supply are intermittent. 

 This may be readily represented by showing the line of change in the 

 degree of vital action on the body during the twenty-four hours, as pro- 

 duced by my own investigations, and delineated in the graphic dia- 

 grams of the present work. 



It is there illustrated that, during the repose of the night, the 

 amount of vital action, as shown by the respiration and pulsation, is 

 low and tolerably uniform, while under the influence of food it is high, 

 and varies during the day extremely, but the general course is such 

 that a large increase takes place after a meal, and a considerable de- 

 crease before the following meal. This increase, followed by decrease, 

 being due to the action of food, proves that the influence is temporary, 

 and that after a sufficient interval another supply of food is required. 



