“ It is not laid on all sales, but only on first or initial sales-those by the manufacturer, producer or importer. Subsequent sales, as where purchasers at first sales resell, are not taxed. Counsel for the government base their contention on the requirement that the tax be paid by 'the manufacturer, producer or importer'; but we think this requirement is intended to be no more than a comprehensive and convenient mode of reaching all first or initial sales, and that it does not reflect a purpose to base the tax in any way on manufacture, production or importation. ”

“ Many hold that whether the burden of any tax paid by the seller is actually passed on to the buyer depends upon considerations so various and complex as to preclude the assumption a priori that any particular tax at any particular time is passed on. ”

“ This principle is implied from the independence of the national and state governments within their respective spheres and from the provisions of the Constitution which look to the maintenance of the dual system. ”

“ In some conditions of the market, the burden remains with the seller, or even may be shifted back from the seller to the producer by the reduction of the producer's price, rather than forward to the consumer by an increase of the seller's price. [6]
Whatever factors determine whether the burden does in fact shift, I do not think it can be said that a tax paid by the seller in any given case necessarily burdens the purchaser either more or less, because in form laid on the sale, as in the Panhandle Oil Case, or upon transportation of goods sold f. ”