Thus a library, to meet the need of our time, must take, and must spread out in a convenient form, a great array of periodicals. Our active practitioners read these by preference over almost everything else. Our specialists, more particularly, depend on the month's product, on the yearly crop of new facts, new suggestions, new contrivances, as much as the farmer on the annual yield of his acres. One of the first wants, then, of the profession is supplied by our library in its great array of periodicals from many lands, in many languages. Such a number of medical periodicals no private library would have room for, no private person would pay for, or flood his tables with if they were sent him for nothing. These, I think, with the reports of medical societies and the papers contributed to them, will form the most attractive part of our accumulated medical treasures. They will be also one of our chief expenses, for these journals must be bound in volumes and they require a great amount of shelf-room; all this, in addition to the cost of subscription for those which are not furnished us gratuitously. It is true that the value of old scientific periodicals is, other things being equal, in the inverse ratio of their age, for the obvious reason that what is most valuable in the earlier volumes of a series is drained off into the standard works with which the intelligent practitioner is supposed to be familiar. But no extended record of facts grows too old to be useful, provided only that we have a ready and sure way of getting at the particular fact or facts we are in search of. And this leads me to speak of what I conceive to be one of the principal tasks to be performed by the present and the coming generation of scholars, not only in the medical, but in every department of knowledge. I mean the formation of indexes, and more especially of indexes to periodical literature.