In this Part of this Act the following expressions have the meanings hereby respectively assigned to them, that is to say:—
" local authority " and " district " have the same meanings as in the Public Health Act 1936 ;
" local health authority " means an authority that is a local health authority for the purposes of Part III of the National Health Service Act 1946 ;
" notifiable disease " means any of the diseases specified in section 47 of this Act.