36 GENERAL SCIENCE 



dangerous are the drugs used for the relief of pain, and so ruinous their 

 long continued use, that under no conditions are they to be employed 

 save by direction of a physician. 



Exercise is indispensable to the maintenance of health and the 

 development of the body. In order to be healthy all organs must be 

 kept active. This is as true of the brain as of other parts of the body. 

 Labor is the price for developing and maintaining a state of health. 

 Work becomes a curse only when its demands on time and strength 

 are excessive, and when one is a slave to it rather than its master. 



INFECTION 



Bacteriology, or the study of microscopic forms of life, 

 is a new science. The story of its discoveries, and of the 

 benefits which already have come to mankind through it, 

 is as fascinating as fiction. Much of the present day 

 knowledge of the effects of living organ'sms of microscopic 

 size, whether one-celled animals known as protozoa or one- 

 celled plants known as bacteria (see page 324), dates from the 

 researches of Louis Pasteur (1822-1895). 



In 1857 the discovery was made by Pasteur (pas'-tur) 

 that fermentation is due to the action of bacteria. In 1886 

 he was successful in his efforts to destroy the bacteria infest- 

 ing the silk worms of France and Italy and threatening the 

 destruction of the silk industry there. But it was when 

 he turned his attention to the study of the causes of those 

 diseases transmitted from one animal to another that the 

 field of medical bacteriology was opened up. 



Some of his first experiments were with chickens affected 

 by cholera, and later with cattle having splenic (splen'-ik) 

 fever. He was able so to reduce the poisonous effects of a 

 virus (poison) containing the germs of a disease that when 

 it was administered to a healthy animal only a mild form 

 of the disease resulted, and the animal became for a time 

 immune to that disease. Here was the beginning of the use 



