ABSTRACT
Lipids include not only true fats but also substances that are chemically related to fats or related to them because of common solubilities as well as possible biological relationships. There are five categories of lipids:
1. Fats-esters of fatty acids and glycerol 2. Waxes-esters of fatty acids and alcohols 3. Phospholipids-fats that contain, in addition, phosphoric acid and nitrog-
enous groups 4. Cerebrosides-combinations of fatty acids, sugars, and nitrogenous substances 5. Sterols-hydrogenated phenanthrene derivatives
The lipids are generally soluble in ether and allied solvents, while carbohydrates are practically insoluble.
