28 APPLIED PHYSIOLOGY 



the food when food tastes just agreeably salt. About one half an ounce 

 needs to be eaten each day. 



32. Lime. A small amount of lime is found every- 

 where in the body, but bone is over one half lime. In all, 

 there are between ten and twelve pounds of lime in the 

 body, but only six grains need be eaten each day. Much 

 more than this amount is found in all common food. The 

 main use of lime is to give stiffness to the bones. It is 

 mixed with the cells and fibers of the bone, just as starch 

 is mixed with the fibers of linen to make it stiff. 



33. The alkalies soda and potash. Some substances 

 are sour and burning to the taste, and can corrode or eat 

 away flesh and metals. When soda or potash is mixed 

 with such a substance, both ingredients in the mixture are 

 changed and a new substance unlike either is formed. 

 For instance, strong vinegar is such a sour, corrosive sub- 

 stance. When soda is added to it the mixture bubbles for 

 a time, and then the liquid is no longer sour or irritating, 

 but has a flat, bitter taste, and both the soda and vinegar 

 have become changed. A substance which is sour to the 

 taste and corrodes metals and flesh, and unites with soda 

 or potash with a bubbling, is called an acid. Soda and 

 potash are called alkalies. They also can corrode certain 

 substances, but they always unite with acids at the first 

 opportunity, and by their union each is changed to a 

 less harmful form. So alkalies destroy or neutralize 

 acids, and acids neutralize alkalies. 



34. Chemical action. When two substances are mixed 

 together so that each becomes changed and substances 

 unlike either are produced, the process is called chemical 

 action. Sugar will dissolve in vinegar, but it still remains 

 sugar, and so the mixture is called a solution (see p. 22). 

 In contrast with it, when soda is dissolved in vinegar it is 



