SOME CHEMISTRY OF EVERYDAY LIFE 175 



means loss in efficiency, even when serious illness does not 

 occur. A physician in times of illness seeks through right 

 hygienic conditions and the use of medicines to restore in 

 his patient those bodily conditions favorable for normal 

 chemical activities. The work done by the cells of the body, 

 and by its various organs, is through chemical changes 

 brought about in them and by them. One value of exercise 

 lies in its direct stimulation of these chemical changes, 

 and in the maintenance of conditions favorable to their 

 accomplishment. Lack of wisely chosen exercise results in 

 an impaired metabolism, and a decrease in bodily vigor and 

 efficiency. 



Fermentation as a common chemical change may be the 

 result of the growth of yeasts as in bread, or of bacteria as in 

 the " mother" of vinegar. In all cases the action of any 

 enzyme or the development of bacteria ceases when un- 

 favorable conditions arise. Oftentimes the life activities 

 of the bacteria themselves produce these unfavorable condi- 

 tions as in the case of the souring of milk and of vinegar. 

 When a certain degree of acidity is reached the action ceases. 

 The acid in the gastric fluid of the stomach is unfavorable for 

 any continued action of the ptyalin of the saliva. 



When the chemical element chlorine (Cl) is liberated from 

 its compounds in the presence of water (H 2 O), so great is the 

 attraction, or affinity, of chlorine for hydrogen that a chemical 

 change is likely to occur between these two elements to form 

 the compound hydrogen chloride, or hydrochloric acid (HC1), 

 with the liberation of the element oxygen (O). 



Under such conditions the free oxygen by reason of its 

 great chemical affinity is likely to unite with whatever may 

 be at hand that is readily oxidized, thus " burning it up" and 

 completely changing its nature. Organic matter in solution 

 in drinking waters is likely to cause sickness, and disease 

 germs are sometimes present in water for household uses. 



