It is already known that in the case of dental caries or periodontal diseases (alveolar pyorrhea, in particular), the two most popular dental diseases, a change is brought about in the environmental factors in the oral cavity, or reversely, in case of a change taking place in the environmental factors in the oral cavity, these diseases are very apt to be contracted.Many studies are now being conducted concerning the acti vity of these diseases. Several methods of testing the activity of dental caries have been devised and they are now being widely employed clinically. However, no similar progress has so far been witnessed in the field of alveolar pyorrhea.Thus, for the purpose of investigating clinically the difference in the immunochemical factors in the whole saliva (hereinafter referred to merely as the saliva), in connection with the above-mentioned dental diseases, the present writer has undertaken an investigative experiment by means of the method of plate agar diffusion.Namely, the supernatants and deposits of the centrifuged salivas from pyorrhea, caries-free (DMF above 5) and normal subjects, respectively, were injected into rabbits as antigen to immunise the animals, and their serum and their reaction to each collected saliva were examined by the method of plate agar diffusion.The conclusions obtained were as follows:1. The serum vaccinated with each supernatant of saliva as antigen collected from subjects reacted against each saliva. The reaction indicated a precipitated zone and was positive. In no case, the supernatant or the deposit alone was seen to be positive.2. The behaviors of the saliva from subjects in case of a positive precipitation and the serum obtained from the deposits as antigen were as shown in the table below.As indicated by the table, the rate of positive precipitation with the saliva of the same kind with the antigen from which the vaccinated serum was obtained was seen to be higher as compared with others. Especially, in the case of alveolar pyorrhea, this feature was strongly indicated.3. In particular, the factors of precipitated reaction of saliva collected from alveolar pyorrhea were sought. As a result, it was found that these factors were in the supernatant of saliva but not in the deposit. Besides, these factors were not dialyzable.4. The precipitated reaction between the condensed synthetic medium, in which the micro-organisms having the gelatin liquefaction ability isolated from the saliva of alveolar pyorrhea were cultured, and each of the serum obtained from the supernatant and deposit of the saliva of alveolar pyorrhea, as antigen, was examined, and, as a result, the following was known:No positive precipitation was indicated with every strain only. However, a slight precipitation was seen to be indicated with the mixed several strains. From the groups of positive precipitation, rodform bacteria of genus pseudomonas and coccus-form bacteria of genus micrococcus were invariably found.In view of the above results achieved, the present writer is strongly confident that the method of plate agar diffusion is highly effective in diagnosing alveolar pyorrhea and also that the saliva may effectively be used for the examination of its prognosis.