“ It is a mere matter of choice of convenient remedy for a state to permit its courts to enjoin the collection of a state tax because it is illegal or unconstitutional. Very different considerations arise where courts of a different, though paramount, sovereignty, interpose in the same manner and for the same reasons. ”

“ An examination of the decisions of this court shows that a proper reluctance to interfere by prevention with the fiscal operations of the state governments has caused it to refrain from so doing in all cases where the Federal rights of the persons could otherwise be preserved unimpaired. It has been held uniformly that the illegality or unconstitutionality of a state or municipal tax or imposition is not of itself a ground for equitable relief in the courts of the United States. ”

“ As long ago as 1879 the supreme court of the state, in holding that the invalidity of a tax afforded no ground for enjoining its enforcement, said of this statute: 'Against an illegal tax, complainant has a full and adequate remedy at law ”