MATTER AND ENERGY 83 



and sugars. They consist of carbon, hydrogen 

 and oxygen, the two latter elements being in 

 the proportions that form water, that is, 

 two of hydrogen to one of oxygen, hence the 

 somewhat inappropriate name. They contain 

 no nitrogen. They are usually classified into 

 the polysaccharides, such as starch and glyco- 

 gen (an animal starch found in the liver), 

 monosaccharides, such as dextrose, glucose or 

 grape sugar ; and disaccharides, such as cane 

 sugar, lactose, and maltose. When cane 

 sugar is inverted, it takes up water and is 

 changed into equal parts of dextrose (grape 

 sugar) and levulose (fructose). By hydro- 

 lysis of starch various forms of dextrin are 

 formed. Cellulose, as found in the cell- 

 walls of plants, is also a carbo-hydrate. 

 Carbo-hydrates, by various chemical agencies, 

 may also be resolved into simple substances, 

 and ultimately into carbonic acid and water. 

 41. The Fats consist of a combination of 

 a fatty acid and glycerine. They consist of 

 carbon, hydrogen, and oxygen, but the amount 

 of carbon present in proportion to the oxygen 

 present is much greater than in carbo- 



