DR. L. E. CUSTER, Dayton. Ohio:—Before we can understand the action of the oral fluids upon the cement, or the action of the cement upon the tooth structure, we must first get an idea of what oxyphosphate of zinc is. When the two portions are united, the powder has such an influence upon the fluid as to cause it to crystallize, which in turn incorporates the powder in it. It is a chemical reaction so far as the liquid changes its form to a liquid of crystallization and also liberates heat, but it is a mixture as the powder does not change its form—it is still oxide of zinc. Being of this nature, it is easily acted upon by external agents, and at the same time the free phosphoric acid acts upon the tooth structure. He had found that alkalies acted upon the cement by neutralizing the acid of crystallization, which liberated the oxide of zinc as a precipitate. Strong acids overpower the phosphoric acid and act upon the oxide, the latter disappearing in the solution. So, as had been referred to by Dr. Cassidy, we will find a more rapid loss in mouths in which putrefaction is going on, because putrefaction being distinguished from fermentation only by the presence of nitrogen, and it has been shown by Dr. Watt that one stage in the formation of nitric acid was the formation of ammonia. Ammonia disintegrates the cement by neutralizing the acid of crystallization. DR. ARNOLD said he filled roots with oxychloride by using fibres of cotton on a small broach. DR. MCKELLOPS defied anyone to fill pulp canals with oxychloride of zinc, as well as with a solution of gutta-percha. He said there was often more than _one_ opening at the apex. He can tell when the gutta-percha has reached the apex by watching the countenance of the patient. DR. GRAY said he enlarged the root canal and filled with iodoform and oil of cassia. DR. F. A. HUNTER, Cincinnati, Ohio, said he was never sure that he filled but two roots perfectly, and those were where the gutta-percha appeared at the opening of the sinus leading from the roots. DR. W. H. SILLITO, Xenia, Ohio, asked if it was not the oxychloride of zinc which had the therapeutic effect. The annual election of officers ensued with the following result: President. Dr. M. H. Fletcher, Cincinnati; First Vice-President, Dr. L. E. Custer, Dayton; Second Vice-President, Dr. Otto Arnold, Columbus; Corresponding Secretary, Dr. H. T. Matlack, Covington, Ky.; Recording Secretary, Dr. H. T. Smith, Cincinnati; Treasurer, Dr. Frank A. Hunter. Cincinnati. (TO BE CONTINUED.) Colleges. MISSOURI DENTAL COLLEGE. The commencement exercises of the Missouri Dental College were held in Memorial Hall, on the evening of March 13th, 1890, in connection with the St. Louis Medical College. Prof. Alleyne, M.D., dean of the latter college, conferred the degree of M.D. upon twenty-two graduates. Prof. W. H. Eames, D.D.S., conferred the degree of D.D.S. upon the following gentlemen: