560 APPLIED BIOLOGY 



established; vaccination required; spitting on walks pro- 

 hibited; and still other measures in the interest of public 

 health put into legal operation. Such is the field of public 

 hygiene and the work of health officials, who aim to apply 

 biological principles and Protect the citizens in numerous 

 cases where individuals c. f mot protect themselves. Every 

 citizen should get acquainted with the health laws in his 

 locality and then cooperate with the officials whose duty 

 it is to get the laws enforced. 



