After twenty-five years of stubborn fight supporters of gold as a filling for decayed teeth accept the possibility of plastic material being in certain cases its superior; throughout this period I have been content to hold my peace and act entirely on my own judgment in the selection of material, as however, it seems to be the fact that a man who uses plastic filling without danger of being termed a “quack,” may speak, I would, through your kind agency, convey to brother Dentists my method of preparing metallic amalgams, which has saved me much trouble and my patients a large number of teeth. In using amalgam, the first thing we ought to take into consideration is whether that which we are using and calling by that name is such, and I venture to say that in a very large number of cases it is no amalgam at all, but a concrete admixture of solid metals with liquid mercury. In the early days, when metallic precipitate of silver was employed, perfect amalgamation was not difficult to obtain, provided the precipitate had been in the first instance properly washed and carefully stoppered, the minute sub-division of the metal and absence of oxidation aiding largely to this result. The fillings of the present day are of a totally different character, coarse in grain, and of a nature to oxidize on even momentary contact with air, they become difficult to amalgamate with mercury, which, in itself, is a highly oxidizable metal, so that recourse is often had to a glass tube and violent agitation to produce that which is at best only a semblance of what it should be—a thoroughly homogeneous mass, that upon setting will retain a uniform texture and density proportionate to the constituents of which the fillings are composed. If, however, to the fillings and mercury be added a drop or less of sulphuric acid, either in the palm of the hand or mortar, it will be found that the metals will almost instantaneously amalgamate, whilst the oxides combining with the acid leave a residuum which, by its quantity, clearly shows what a very imperfect body could have been a so-called amalgam containing only a small portion of them. Washing in pure water at once removes all trace of acid, and a thoroughly reliable stopping can be at once produced from materials otherwise worse than useless. Introductory Lecture to Course on Dental Mechanics. BY DR. J. WALKER. GENTLEMEN,—The authorities of the Dental Hospital of London have entrusted to me the heavy responsibility of lecturing on Dental Mechanics for this present Session of 1880 and 1881. I have undertaken this post with many misgivings; the subject is so wide and comprehensive, the study so important to you now, and the effect of good or bad teaching will so deeply affect your whole life, that I might well have hesitated before finally accepting the duties that will now devolve upon me.