Whenever the Mayor shall be satisfied that rabies has appeared among the dogs of the City, he shall issue a proclamation requiring all persons to confine their dogs or to have the same securely muzzled, for such time from and after the issuing of such proclamation as he shall therein appoint. If any dog shall be found at large in the City, during the time so appointed, without being properly and securely muzzled, such dog may be killed. The owner or keeper of a dog so at large shall be guilty of misdemeanor.