382 THE ANIMALS AND MAN 



treme precautions against it. Gradually physicians and 

 bacteriologists are discovering means of making people 

 immune or thoroughly resistant to diseases. The first step 

 in these discoveries is the thorough investigation of the 

 disease and the nature of its cause. The next step is to 

 find out what substance will, if inoculated or injected into 

 the blood, serve as an effective preventive of the disease. 



Immunity from smallpox was discovered over a hundred 

 years ago in the use of the comparatively harmless vaccine 

 or virus of cowpox. This was a great discovery and its use 

 has prevented the spread of many epidemics of smallpox. 

 The discovery of the use of antitoxin for the cure and pre- 

 vention of diphtheria has also been of great benefit to man- 

 kind. As science advances, other such means of producing 

 artificial immunity fro"tai disease will be discovered until infec- 

 tious disease will come to be largely under the control of man. 



Public hygiene and sanitation. — In a large commimity, 

 there are always a great many careless and ignorant people. 

 It therefore becomes necessary to appoint boards and officers 

 to look after the public health. It is the duty of a board of 

 health, through its officers, to examine all the conditions af- 

 fecting the health of the people at large. It must examine 

 public supplies such as milk, water, ice, meats, etc. It must 

 examine the dairies that furnish milk to the community, 

 see that the cows are healthy, the buildings clean, and that 

 the milk pails and pans are thoroughly sterilized, etc. It 

 must look after the water supply, to be sure that there is no 

 opportunity for its contamination with impurities. It must 

 inspect the markets to see that no tainted meats or other 

 dangerous foods are offered for sale. It must see that the city 

 is well drained and that the sewers of houses are properly 

 connected with the city drainage system. In short, a health 

 board must take charge of everything that affects the health 

 of the people, and hence its duties are many and of the 

 utmost importance. 



