HUMAN STRUCTURE AND LIFE-ACTIVITIES 463 



pressed from cane and beet ; and by refining processes, these 

 dark-colored sugars are made into the " soft white " and 

 " granulated " sugars. Maple sugar, from the sap of maple 

 trees, is chemically the same as cane-sugar, but flavored 

 with peculiar substances found in the maple sap. 



379. Fats. This includes all kinds of fats and oils from 

 animals and plants. Common examples are butter, lard, 

 beef -suet or tallow, olive oil, cotton-seed oil, fat of meats, oil 

 of nuts. Like the sugars and starches (carbohydrates), fats 

 contain only three elements : carbon, hydrogen, and oxygen. 

 The sugars, starches, and fats taken together are often called 

 " non-nitrogenous foods," because they have no nitrogen. 



380. Proteins. Formerly spelled " proteids." White- 

 of-egg (" egg-albumen "), lean meat, and milk curds have 

 abundant proteins. They contain carbon, hydrogen, nitro- 

 gen, oxygen, and sulphur. Also, some have phosphorus and 

 iron. It appears then that all proteins differ from carbo- 

 hydrates and fats in having nitrogen and sulphur. As already 

 stated, only plants can make proteins, and animals must get 

 them directly or indirectly from plants. 



381. Albuminoids. This term, which means albumen- 

 like, is applied to certain food substances which have the 

 composition of proteins (formerly called albumens) . Gelatin 

 is the most common example. The finer quality used for 

 human food, for photographic plates, and for bacteriological 

 study is obtained by cooking connective tissues, tendons, and 

 marrow of bones. Pigs' feet, which are by many people 

 considered a delicacy, produce much gelatin when boiled. 

 Common furniture glue is a crude gelatin from the connective 

 tissue of the hides and hoofs of animals. Fish glue is a gelatin 

 made from the delicate membranes of the air-bladders of fishes. 

 Common gelatin is the only albuminoid used extensively for 

 human food. Although having the composition of proteins, 

 gelatin cannot take their place as food. Dogs have been 

 found to live well with only protein foods (e.g., lean meat); 



