From Merchants' Loan & Trust Co v Smietanka (1921), 255 US 509. The court referred to several post-ratification cases and to the 1909 (pre-ratification) Corporation Excise Tax Act, and said:-

'There can be no doubt that the word ["income"] must be given the same meaning and content in in the Income Tax Acts of 1916 and 1917 that it had in the Act of 1913. When to this we add that in Eisner v Macomber, supra, a case arising from the same Income Tax Act of 1916 which is here involved, the definition of "income" which was applied was adopted from Stratton's Independence v Howbert, supra, arising under the Corporation Excise Tax Act of 1909, with the addition that it should include "profit gained through the sale or conversion of capital assets", there would seem to be no room to doubt that the word must be given the same meaning in all of the Income Tax Acts of Congress that was given to it in the Corporation Excise Tax Act and that what that meaning is has now become definitely settled by decisions of this Court.'

Since that 1909 Act imposed an excise tax upon corporate profits, it is "definitely settled" that "income" for tax purposes consists of corporate profits. This is entirely consistent with the earlier Brushaber opinion that Amendment 16 gave Congress "no new taxing power."