Book 5
17
17 The powers of medicaments when unmixed having been set out, we have to say how how they may be mixed together, and what are the compositions so made. Now they are mixed in various ways and there is no limit to this, since some simples may be omitted, others added, and when the same ingredients are used the proportion of their weights may be changed. Hence though there are not so very many substances having medicinal powers, there are innumerable kinds of mixtures; and, even if all of them could be included, yet this would be needless. For the same effects are produced by but a few compositions, and to vary these is easy to anyone who knows their powers. Therefore I shall content myself with those I have heard of as the best known. Now in this book I will set forth those compositions which may have been required in the previous treatments or which pertain to those treatment with which I am going shortly to mention here, so that I may bring together at the same time compositions which are more generally used: those that are applicable to a particular disease, or even to a few, I shall mention in their appropriate places. But I wish to make clear in advance that our uncia has the weight of seven denarii, next that I divide one denarius by weight into six parts, namely, sextantes; so that I have in the sextans of a denarius the same weight as the Greeks have in what they call an obolus. That being reduced to our weight, takes the obolus a little more than half a scripulus.
