Alexander, the seventh bishop of Rome, who introduced holy water both into houses and churches for spiritual purposes, made some alterations in the ingredients of the Eucharist, by mixing water with the wine, and by substituting unleavened for common bread. In the time of Irenaeus and Justin the Martyr, we find an account of the Eucharist as it was then thought of and celebrated. Great stress was then laid upon the bread and wine as a holy and sacramental repast: prayers were made that the Holy Ghost would descend into each of these substances. It was believed that it did so descend; and that as soon as the bread and wine perceived it, the former operated virtually as the body, and the latter as the blood of Jesus Christ. From this time the bread was considered to have great virtues; and on this latter account, not only children, but sucking infants, were admitted to this sacrament. It was also given to persons on the approach of death. And many afterwards, who had great voyages to make at sea, carried it with them to preserve them both from temporal and spiritual dangers. In the twelfth century, another notion, a little modified from the former, prevailed on this subject; which was, that consecration by a Priest had the power of abolishing the substance of the bread, and of substituting the very body of Jesus Christ. This was called the doctrine of Transubstantiation. This doctrine appeared to Luther, at the dawn of the reformation, to be absurd; and he was of opinion that the sacrament consisted of the substance of Christ's body and blood, together with the substance of the bread and wine; or, in other words, that the substance of the bread remained, but the body of Christ was inherent in it, so that both the substance of the bread and of the body and blood of Christ was there also. This was called the doctrine of Consubstantiation, in contradiction to the former. Calvin again considered the latter opinion erroneous: he gave it out that the bread was not actually the body of Jesus Christ, nor the wine his blood; but that both his body and blood were sacramentally received by the faithful, in the use of the bread and wine. Calvin, however, confessed himself unable to explain even this his own doctrine. For he says, "if it be asked me how it is, that is, how believers sacramentally receive Christ's body and blood? I shall not be ashamed to confess, that it is a secret too high for me to comprehend in my spirit, or explain in words." But independently of the difficulties which have arisen from these different notions concerning the nature and constitution of the Lord's supper, others have arisen concerning the time and the manner of the celebration of it.