Excerpt taken from the Catholic Encyclopedia on January 2007: Title "Communion under Both Kinds" 
Full document http://www.newadvent.org/cathen/04175a.htm

CATHOLIC DOCTRINE AND MODERN DISCIPLINE

(1) Under this head the following points are to be noted: (a) In reference to the Eucharist as a sacrifice, the communion, under both kinds, of the celebrating priest belongs at least to the integrity, and, according to some theologians, to the essence, of the sacrificial rite, and may not therefore be omitted without violating the sacrificial precept of Christ: "Do this for a commemoration of me" (Luke 22:19). This is taught implicitly by the Council of Trent (Sess. XXI, c. i; XXII, c. i). (b) There is no Divine precept binding the laity or non-celebrating priests to receive the sacrament under both kinds (Trent, sess. XXI, c. i.)

(c) By reason of the hypostatic union and of the indivisibility of His glorified humanity, Christ is really present and is received whole and entire, body and blood, soul and Divinity, under either species alone; nor, as regards the fruits of the sacrament, is the communicant under one kind deprived of any grace necessary for salvation (Trent, Sess. XXI, c., iii). (d) In reference to the sacraments generally, apart from their substance, salva eorum substantia, i.e. apart from what has been strictly determined by Divine institution or precept, the Church has authority to determine or modify the rites and usages employed in their administration, according as she judges it expedient for the greater profit of the recipients or the better protections of the sacraments themselves against irreverence. Hence "although the usage of Communion under two kinds was not infrequent in the early ages [ab initio] of the Christian religion, yet, the custom in this respect having changed almost universally [latissime] in the course of time, holy mother the Church, mindful of her authority in the administration of the Sacraments, and influenced by weighty and just reasons, has approved the custom of communicating under one kind, and decreed it to have the force of a law, which may not be set aside or changed but by the Church's own authority" (Trent, Sess. XXI, c. ii). Not only, therefore, is Communion under both kinds not obligatory on the faithful, but the chalice is strictly forbidden by ecclesiastical law to any but the celebrating priest.

These decrees of the Council of Trent were directed against the Reformers of the sixteenth century, who, on the strength of John, vi, 54, Matt., xxvi, 27, and Luke, xxii, 17, 19, enforced in most cases by a denial of the Real Presence and of the Sacrifice of the Mass, maintained the existence of a Divine precept obliging the faithful to receive under both kinds, and denounced the Catholic practice of withholding the cup from the laity as a sacrilegious mutilation of the sacrament.

A century earlier the Hussites, particularly the party of the Calixtines, had asserted the same doctrine, without denying, however, the Real Presence or the Sacrifice of the Mass, and on the strength principally of John, vi, 54; and the Council of Constance in its thirteenth session (1415) had already condemned their position and affirmed the binding force of the existing discipline in terms practically identical with those of Trent (see decree approved by Martin V, 1418, in Denzinger, Enchiridion, n. 585). It is to be observed that neither council introduced any new legislation on the subject; both were content with declaring that the existing custom had already acquired the force of law. A few privileged exceptions to the law and a few instances of express dispensation, occurring later, will be noticed below (II).

(2) Regarding the merits of the Utraquist controversy, if we assume the doctrinal points involved -- viz. the absence of a Divine precept imposing Communion under both kinds, the integral presence and reception of Christ under either species, and the discretionary power of the Church over everything connected with the sacraments that is not divinely determined the question of giving or refusing the chalice to the laity becomes purely practical and disciplinary, and is to be decided by a reference to the two fold purpose to be attained, of safeguarding the reverence due to this most august sacrament and of facilitating and encouraging its frequent and fervent reception. Nor can it be doubted that the modern Catholic discipline best secures these ends. The danger of spilling the Precious Blood and of other forms of irreverence; the inconvenience and delay in administering the chalice to large numbers -- the difficulty of reservation for Communion outside of Mass: the not unreasonable objection on hygienic and other grounds, to promiscuous drinking from the same chalice, which of itself alone would act as a strong deterrent to frequent Communion in the case of a great many otherwise well-disposed people; these and similar "weighty and just reasons" against the Utraquist practice are more than sufficient to justify the Church in forbidding it.

Of the doctrinal points mentioned above, the only one that need be discussed here is the question of the existence or non-existence of a Divine precept imposing Communion sub utraque. Of the texts brought forward by Utraquists in proof of such a precept, the command, "Drink ye all of this" (Matthew 26:27), and its equivalent in St. Luke (xxii, 17, i.e. supposing the reference here to be to the Eucharistic and not to the paschal cup), cannot fairly be held to apply to any but those present those on the occasion, and to them only for that particular occasion. Were one to insist that Christ's action in administering Holy Communion under both kinds to the Apostles at the Last Supper was intended to lay down a law for all future recipients, he should for the same reason insist that several other temporary and accidental circumstances connected with the first celebration of the Eucharist (e.g. the preceding paschal rites, the use of unleavened bread, the taking of the Sacred Species by the recipients themselves) were likewise intended to be obligatory for all future celebrations.

The institution under both kinds, or the separate consecration of the bread and wine, belongs essentially, in Catholic opinion, to the sacrificial, as distinct from the sacramental, character of the Eucharist; and when Christ in the words "Do this for a commemoration of me" (Luke 22:19), gave to the Apostles both the command and the power to offer the Eucharistic sacrifice, they understood Him merely to impose upon them and their successors in the priesthood the obligation of sacrificing sub utraque. This obligation the Church has rigorously observed.

Please take some of your precious time and visit

Communion

The Doctrine of Life in Spirit and Truth
With visionary dreams of the
Body and Blood of Jesus Christ.