8 mechanism to determine the compatibility or otherwise of a reservation with the object and purpose of a given treaty 22, but - even more gravely - do not impede either that certain reservations or restrictions formulated (in the acceptance of the jurisdiction of the organs of international protection) 23 come to hinder the operation of the mechanisms of international supervision created by the human rights treaties in the exercise of the collective guarantee. 27. The present system of reservations, reminiscent of the old Pan-American practice, rescued by the International Court of Justice 24 and the two Vienna Conventions on the Law of Treaties, for having crystallised itself in the relations between States, not surprisingly appears entirely inadequate to the treaties whose ultimate beneficiaries are the human beings and not the Contracting Parties. Definitively, human rights treaties, turned to the relations between States and human beings under their jurisdiction, do not bear a system of reservations which approaches them as from an essentially contractual and voluntarist perspective, undermining their integrity, allowing their fragmentation, leaving at the discretion of the Parties themselves the final determination of the extent of their conventional obligations. 28. As the two Vienna Conventions of 1969 and 1986 do not provide any indication for an objective application of the criterion of the compatibility or otherwise of a reservation with the object and purpose of a treaty, they leave it, on the contrary, to be applied individually and subjectively by the Contracting Parties themselves, in such a way that, at the end, only the reserving State knows for sure the extent of the implications of its reservation. Despite the efforts in expert writing to the effect of systematizing the practice of States on the matter 25, it is difficult to avoid the impression that such practice has been surrounded by uncertainties and ambiguities, and has remained inconclusive to date. This indefinition is not at all reassuring for human rights treaties, endowed as they are with mechanisms of international supervision of their own. This general picture of indefinition has thus, not surprisingly, 22 . As neither the aforementioned Vienna Conventions, nor - prior to them - the cited Advisory Opinion of the International Court of Justice on Reservations to the Convention against Genocide, define what constitutes the compatibility or otherwise (of a reservation) with the object and purpose of a treaty, the determination is left to the interpretation of this latter, without it having been defined either on whom falls that determination, in what way and when it should be made. At the time of the adoption of that Advisory Opinion (1951), neither the majority of the Hague Court, nor the dissenting Judges on the occasion, foresaw the development of the international supervision of human rights by the conventional organs of protection; hence the insufficiencies of the solution then advanced, and endorsed years later by the two Vienna Conventions on the Law of Treaties referred to. 23 . There is a distinction between a reservation stricto sensu and a restriction in the instrument of acceptance of the jurisdiction of an international supervisory organ, even though their legal effects are similar. 24 . The Advisory Opinion of the ICJ on the Reservations to the Convention against Genocide (1951) marked the gradual passage, in the matter of reservations to treaties, from the rule of unanimity (of its approval by the States Parties), to the test of its compatibility with the object and purpose of the treaty. In a general way, the Vienna Convention incorporated the flexible Pan-American doctrine on reservations, in accordance with a tendency to this effect of the international practice already formed in the epoch; I.M. Sinclair, "Vienna Conference on the Law of Treaties", 19 International and Comparative Law Quarterly (1970) pp. 47-69; and cf. Articles 19-20 of the Vienna Convention. 25 . Cf., e.g., J.M. Ruda, "Reservations to Treaties", 146 Recueil des Cours de l'Académie de Droit International de La Haye (1975) pp. 95-218; D.W. Bowett, "Reservations to Non-Restricted Multilateral Treaties", 48 British Year Book of International Law (1976-1977) pp. 67-92; P.-H. Imbert, Les réserves aux traités multilatéraux, Paris, Pédone, 1979, pp. 9-464; K. Holloway, Les réserves dans les traités internationaux, Paris, LGDJ, 1958, pp. 1-358; K. Zemanek, "Some Unresolved Questions Concerning Reservations in the Vienna Convention on the Law of Treaties", Essays in International Law in Honour of Judge Manfred Lachs (ed. J. Makarczyk), The Hague, Nijhoff, 1984, pp. 323-336; Ch. Tomuschat, "Admissibility and Legal Effects of Reservations to Multilateral Treaties", 27 Zeitschrift für ausländisches öffentliches Recht und Völkerrecht (1967) pp. 463-482; F. Horn, Reservations and Interpretative Declarations to Multilateral Treaties, Uppsala, Swedish Institute of International Law, 1988, pp. 184-222.