STRUCTURE OF THE HUMAN BODY 35 



further analysed, is found to contain the four elements, Carbon, 

 Hydrogen, Oxygen, and Nitrogen. It is therefore to be expected 

 that our food should consist in the main of compounds of the 

 same four chemical elements^, and this is actually the case. 

 Obviously this must be so for the fleshy part of the food, and 

 it is also true for the vegetable portion. The different kinds 

 of food may be classified as follows: — 



1 . Nitrogenous Food, consisting, in ultimate analysis, of carbon, 

 hydrogen, oxygen, and nitrogen, together with sulphur, and in 

 some cases phosphorus. Such foods are of exceedingly complex 

 chemical nature, and may broadly be called proteids or albuminoids'^. 

 The last name is taken from albumin, of which white of &^^ 

 may be considered as a type; while egg-yolk, lean meat, blood, 

 gelatin, and cheese are of the same nature in whole or part. 

 An example from the vegetable kingdom is gluten, the sticky 

 constituent of flour, to which the tenacious character of dough 

 is chiefly due. 



2. Non-nitrogenous Food, as the name indicates, contains no 

 nitrogen. Its various kinds are: — 



{a) Carbohydrates, containing carbon, hydrogen, and oxygen, 

 and including starch, sugar, gum, &c. 



(^) Hydrocarbons, or fats and oils, consisting of the same 

 three elements, arranged, however, in different proportions. 



(c) Mineral Salts, including compounds of lime and iron, as 

 well as common salt (sodium chloride). The more complicated 

 foods enumerated under the preceding headings contain a vary- 

 ing amount of such mineral compounds, which have, however, 

 to be supplemented in Man and various other animals by com- 

 mon salt. The importance of salts of lime becomes apparent 

 when we remember that the hard part of bones and teeth 

 consists of them. 



{d) Water, consisting of hydrogen and oxygen, and generally 

 containing mineral salts dissolved in it. Water is not only taken 

 in the form of drink, but also forms an important constituent of 

 albuminous, starchy, and fatty foods. 



This complex food, unlike the food of plants, which is entirely 

 gaseous or liquid, is largely taken into the body in the form of 



'■ A chemical element is a substance which cannot, so far as we know, be resolved into com- 

 ponents of different nature. 



"^ The term albuminoid is often ijsed in a narrower sense than this. 



Vol. I. 3 



