It shall be unlawful for any person, firm or corporation to keep or cause to be kept any swine in the City and County of San Francisco except as follows:
For the sole purpose of loading, unloading, feeding and slaughtering of swine, the provisions of this section shall not apply to that part of the city and county bounded and described as follows:
Starting at the point of intersection of the southwesterly line of Arthur Avenue with the southeasterly line of Third Street or Railroad Avenue; then continuing along Arthur Avenue to the intersection with the northwesterly line of Keith Street; thence southeasterly along Keith Street to the northeasterly line of Fairfax Avenue; thence northwesterly along the northeasterly line of Fairfax Avenue to the southeasterly line of Third Street, also called Railroad Avenue; and thence northeasterly to Arthur Avenue and point of commencement; provided, that all buildings and structures shall be built and maintained in accordance with the building laws applicable thereto; and provided, further, that a certificate of sanitation shall be obtained from the Director of Public Health for the maintenance or operation of said business or premises, and further provided that no swine shall be kept upon said premises or within the City and County of San Francisco for a period longer than 30 days.