430 THE HUMAN BODY 



(a protein), some fats, much starch, and a little sugar; all true 

 food stuffs: but mixed with these is a quantity of cellulose (the 

 chief chemical constituent of the walls which surround vegetable 

 cells), and this is not a true food since it is incapable of digestion. 

 Chemical examination of all the common articles of diet shows 

 that the actual number of important food stuffs is but small: 

 they are repeated in various proportions in the different things we 

 eat, mixed with small quantities of different flavoring substances, 

 and so give us a pleasing variety in our meals; but the essential 

 substances are much the same in the fare of the workman and 

 in the "delicacies of the season." These primary food stuffs, 

 which are found repeated in so many different foods, belong to one 

 or the other of the classes of nutrients mentioned above; and the 

 food value of any article of diet depends on them far more than on 

 the traces of flavoring matters which cause certain things to be 

 especially sought after and so raise their market value. We 

 cannot, however, conclude that the possession of flavor by foods 

 is wholly unnecessary. We shall see it plays a very real and very 

 important role in our use of foods in general. 



The Inorganic Essential Accessories. Two inorganic sub- 

 stances, water and sodium chlorid (common salt), are taken 

 separately and consciously as constituents of the diet. We re- 

 quire such large amounts of these substances that they have to be 

 taken thus purposely to insure that enough be gotten. The other 

 inorganic materials, the chlorids, phosphates, and sulphates of 

 potassium, magnesium, and calcium, occur in most ordinary arti- 

 cles of diet, so that we do not swallow them in a separate form. 

 Phosphates, for example, exist in nearly all animal and vegetable 

 foods; moreover certain foods, as casein, contain phosphorus in 

 combinations which in the Body yield it up to be oxidized to form 

 phosphoric acid. The same is true of sulphates, which are par- 

 tially swallowed as such in various articles of diet, and are partly 

 formed in the. Body by the oxidation of the sulphur of various pro- 

 teins. Calcium salts are abundant in bread and milk, and are also 

 found in many drinking-waters. That these salts are essential to 

 life is proven by the results of feeding animals on diets which 

 have been carefully made salt-free, but are otherwise fully ade- 

 quate. Such diets invariably cause a steady decline, and, if not 

 discontinued, death. The remarkable fact is that under these 



