POLICE POWER 21 



been given, and the general lorinciples under which 

 it operates may cause expansion or contraction of 

 its application upon the same general subject un- 

 der different circumstances. To prevent harm 

 being done by unqualified or unprincipled practi- 

 tioners of medicine or surgery, under police power 

 the doctor may be compelled to present evidence 

 of his fitness for the trust, and in order to cany 

 out this provision the state may prohibit any per- 

 son from attempting to treat the sick or injured 

 animals of any species until he shall first have 

 obtained a license. Under police power quaran- 

 tines are established, the production and sale of 

 foods are regulated, industrial enterprises are 

 supei'vised, the construction of buildings is con- 

 trolled, the breeding of flies, mosquitoes, rats and 

 other pests is restricted, and trade operations are 

 watched to prevent fraud. Under this power stat- 

 utes are enacted by the state, and ordinances by 

 the city. Sometimes it is exerted by an executive 

 officer unsupported by any previous legislation, 

 and it is recognized by the courts. It is a tre- 

 mendous power, which may easily be abused, but 

 its existence and recognition is of the utmost im- 

 portance for the general good. 



12. Police Power Resides in the States. The 

 Ninth and Tenth Amendments to the Federal Con- 

 stitution have generally been interpreted as grant- 

 ing to the individual states the exclusive right to 

 use the police power, and under state regulation 

 this power has been exercised by the towns and 

 cities within its border. Under that interpreta- 

 tion the nation has no authority to exert this 

 power within the different states. Practically the 



