As this conclusion but enforced a regulation as to the mode of exercising power under particular circumstances, it did not in any way dispute the all-embracing taxing authority possessed by Congress, including necessarily therein the power to impose income taxes if only they conformed to the constitutional regulations which were applicable to them. Moreover, in addition, the conclusion reached in the Pollock Case did not in any degree involve holding that income taxes generically and necessarily came within the class of direct taxes on property, but, on the contrary, recognized the fact that taxation on income was in its nature an excise...