A treaty between two States can never invalidate a stipulation of a previous treaty between one of the contracting parties and a third State. Bearing this point in mind, it must be maintained that the United States, being bound by Article III, No. 1, of the Hay-Pauncefote Treaty, had not the power to enter into the stipulation of Article XIX of the Hay-Varilla Treaty by which she granted exemption from payment of tolls to vessels of the Republic of Panama, and that Great Britain is justified in protesting against the enactment of Section 5 of the Panama Canal Act in so far as it exempts vessels of Panama from the payment of tolls. The fact that the right of Panama to demand exemption from payment of tolls for her vessels is one of the conditions under which the Republic of Panama ceded to the United States the strip of territory necessary for the construction, administration, and protection of the Canal, cannot invalidate the previously acquired right of Great Britain to demand equal treatment of the vessels of all nations without any exception whatever. It must be left to the United States and the Republic of Panama to come to an agreement concerning Article XIX of the Hay-Varilla Treaty. Although the United States promised an exemption from tolls which she had no power to grant, the Republic of Panama need not drop her claim to this exemption. Since, however, the grant of the exemption would violate previous treaty rights of Great Britain, the Republic of Panama is at any rate entitled to a claim to an equivalent of the exemption, namely, the refunding, on the part of the United States, of tolls paid by vessels of the Republic of Panama for the use of the Canal. Whether these vessels are exempt from the payment of tolls or can demand to have them refunded, makes very little difference to the Republic of Panama, although Article XIX of the Hay-Varilla Treaty stipulates exemption from, and not the refunding of, tolls. But the case of the vessels of Panama is quite unique, for their exemption from tolls was one of the conditions under which the Republic of Panama ceded to the United States the Canal territory. Great Britain and the United States being the only contracting parties to the Hay-Pauncefote Treaty, and third States not having as yet either by formal accession become parties to this treaty or acquired, by custom, a claim to equal treatment of their vessels, there would seem to be nothing to prevent Great Britain from consenting to the exemption of the vessels of Panama, should she be disposed to do so. X.