14 THE HUMAN BODY 



Fats. The fats all contain carbon, hydrogen, and oxygen, the 

 oxygen being present in small proportion as compared with the 

 hydrogen. Three fats occur in the Body in large quantities, viz.: 

 palmatin (C 61 H 98 O 6 ), stearin (C 61 H 110 6 ), and olein (O 57 H 104 O 6 ). 

 The two former when pure are solid at the temperature of the 

 Body, but in it are mixed with olein (which is liquid) in such pro- 

 portions as to be kept fluid. The total quantity of fat in the Body 

 is subject to great variations, but its average quantity in a man 

 weighing 75 kilograms (165 pounds) is about 2.75 kilograms (6 

 pounds) . 



Each of these fats when heated with a caustic alkali, in the 

 presence of water, breaks up into a fatty acid (stearic, palmitic, or 

 oleic as the case may be), and glycerin. The fatty acid unites with 

 the alkali present to form a soap. 



Carbohydrates. These may be denned as substances composed 

 of carbon, hydrogen, and oxygen, having the number of carbon 

 atoms in each molecule usually six or some multiple thereof, 

 and having the hydrogen and oxygen present in the same propor- 

 tion as in water. The three chief groups are the sugars, starches, 

 and cellulose. 



\ Dextrose or grape sugar (C 6 H 12 6 ) is the most important repre- 

 sentative of the sugars found in the Body. A large part of the food 

 supply is received from the digestive tract into the blood in this 

 form. It occurs constantly in small concentration in the blood 

 and tissues. 



I ' Lactose, the sugar of milk, occurs in considerable quantity in 

 milk. 



' Glycogen or animal starch (C 6 H 10 O 5 ) is the anhydride of grape 

 sugar. This is the form in which the excess of sugar is stored in the 

 body to be drawn upon at need. Dextrose is readily converted 

 into it, and it in turn is easily changed back into sugar. In many 

 respects it resembles common vegetable starch. It is present in the 

 muscles of the Body and in the liver, the latter organ alone con- 

 taining about as much as all the muscles put together. 



Cellulose, the woody fiber of plants, is not found in the Human 

 Body, although a chemically identical substance, tunicin, is found 

 in the bodies of tunicates. 



Organic Non-Nitrogenous Acids. Of these the most important 

 is carbon dioxid (CO a ), which is the form in which by far the 



