442 THE POPULAR SCIENCE MONTHLY. 



which, when introduced into the body, supplies material which renews 

 some structure or maintains some vital process ; and it is distinguished 

 from a medicine in that the latter modifies some vital action, but does 

 not supply the material which sustains such action. 



This is certainly correct so far as relates to the substances which 

 supply nearly all our nourishment, and which the Germans class under 

 the term Nahrungsmittel, but there are certain so-called foods known 

 as Genussmittel, which seem to form a connecting link, in that they in- 

 crease vital actions in a degree far beyond the amount of nutritive 

 material which they supply. They thus resemble certain medicines in 

 their action, but, as they supply a proportion of nutritive material, 

 they should be ranked as foods. 



It is essential to the idea of a food that it should support or in- 

 crease vital actions ; while medicines usually lessen, but may increase, 

 some of them. 



It is not necessary that a food should yield every kind of material 

 which the body requires, for then one might suffice for the wants of 

 man, but that it fulfils one or more of such requirements, so that by a 

 combination of foods the whole wants of the body may be supplied. 

 Neither is it essential that every food should be decomposed or broken 

 up, and its elements caused to enter into new combinations when form- 

 ing or maintaining the structures of the body, since there are some 

 which in their nature are identical with parts of the body, and, being 

 introduced, may be incorporated with little or no change. 



But there are foods which are more valuable to the body than 

 others, in that they supply a greater number of the substances which 

 it requires, and such are known as compound foods, while others, 

 which supply but one element, or which are incorporated without 

 change, may be termed simple foods. Other foods are more valuable 

 because they are more readily changed into the substance of the body, 

 or act more readily and quickly in sustaining vital actions, and these 

 may be called easily-digested or easily-assimilated foods. Others are 

 preferred because they supply a greater quantity of useful nutriment 

 at a less proportionate cost, and are known as economical foods ; and 

 foods varying in flavor are classed as more or less agreeable foods. 



Some foods are classed according to the source whence they are de- 

 rived, as animal and vegetable foods ; and others according to the 

 density of their substance, as fluid and solid foods. 



There are foods which nourish one part of the body only, and 

 others which sustain one chief vital action, and are called flesh-form- 

 ing or heat-forming foods, while others combine both qualities. 



Besides these larger divisions, there are qualities in foods which 

 permit of further classification, such as those which render them par- 

 ticularly fit for different ages, climates, and seasons, and others which 

 possess a special character, as sweetness, acidity, or bitterness. 



There are also effects produced by foods apart from or in addition 



