mously valuable contribution and should never be lost sight of. The title and scope of this paper does not admit of a lengthy discussion of these phases of the treatment of pyorrhea and prophylaxis, and the author feels in closing his paper, that in order not to create the idea in the minds of this audience that he believes surgical treatment of pyorrhea is the Alpha and Omega of the subject, it should be stated that the powers that make for immunity should be always carefully considered. I thank you for your kind invitation to appear before you and for the delightful courtesies that I have received at your hands. ETIOLOGY OF PYORRHEA ALVEOLARIS? A STUDY OF THEIR HABITS. Weston A. Price, M. S., D. D. S., Directing Researches for the Scientific Foundation and Research Commission of the National Dental Association. Le Rue P. Bensing, A. B., Research Assistant, Cleveland, Ohio. A S DIRECTED, by the Scientific ference in the appearance of some orFoundation and Research Commission, this department has been making special investigations to establish methods for the identification and differentiation of pathogenic and non-pathogenic organisms of the mouth and its lesions. This is a preliminary and partial report, made at this time to assist those who are with difficulty, taking up the study of endamebae, to outline some of the as yet unanswered problems relating thereto and to suggest some lines of parallel work for the co-operation of those of the profession who may be in a position to assist in their solution. The problem that is most vitally concerning the dental profession at this moment is, apparently, the relation of endamebic infection to so called pyorrhea alveolaris and the possibility of its cure with emetine. (1) The microscopic study is one essential line of approach and in order to provide a correct conception of what may be seen in the microscopic field, we will first review the characteristics of the living organisms. We should see and study reproductions of them which reveal their normal individualities, including not only their physical forms but also their natural movements in life's processes. There is as much dif ganisms, when living normally and when dried and stained, as in the swimming swan or the bounding deer when seen at home in their haunts or when their skins are hanging in a tannery. We can learn to identify the swan or the deer by their skins in the tannery or the organisms of the mouth in the stained slide, but we have not learned to know them and their individualities, manners and habits until we have become familiar with them in their natural environments. We have found the motion pictures to be by far the best means for studying the habits of mouth organisms, for by this method we can make them do the same act over and over, with normal rapidity or with any desired slowness. While our studies have included various organisms of the mouth, we will present here chiefly studies of the normal vital motions of the endamebae and their relations to pyorrhea alveolaris. Unfortunately, it is impossible to adequately illustrate in still pictures what is shown in motion pictures, however, a good idea can be gotten by taking out pictures from the series at definite intervals. As indicated, nearly all of these shown are selected at onehalf second intervals of time, where the pictures are taken 16 to 20 per minute. In these shown, however, we have en Endameba buccalis. Unstained living organism, showing its motility and progressive changes of pseudopods as recorded at half second periods for twelve seconds. (See text.) species predominating may vary with the location and the time of the year, in the same mouth under certain conditions, as indicated later. Fig. 1 shows a typicai endameba (1) buccalis of Prowazek (1904) (2) which is probably the same as endameba buccalis of Sternberg (1862), (3) the ameba dentalis of referred to later. Its size varies from 6 to 30 microns (one four thousandth to one eight hundredth of an inch in diameter.) When active it throws out a few lobose pseudopods, which have a definite independent tho consecutive movement which is clearly shown in these unstained illustrations from life. This Fig. Endameba buccalis. Illustrating nuclei, ingested matter and bacteria, also at A and B the ectoplasm and ectosarc. are downward, first toward the right and then toward the left. In the third row the upper border has changed but little, but the thrust is farther towards the left and in the fourth row, while the lower border remains about constant, the motion has been exerted again successively more and more in an upward direction. During this time, the endosarc, including the granular mass within has changed relatively little as shown by the location of its nuclei and ingested material. The red blood corpuscles shown in the three upper rows give a good conception of the relative size of the endameba. With this species the pseudopod is sel Half second intervals. short blunt pseudopod with its limiting membrane, and letter A, its glassy hyaline ectoplasm. They have a slightly yellowish tint, giving a color between that of a leukocyte and a red blood cell. Frequently in extra good specimens the ectosarc with its contained protoplasm seems to be relatively large in proportion to its contained granular endosare and gives the appearance that the latter is floating within it. In these specimens there are usually several very large blunt pseudopods present at once, tho note, as previously stated, only one is motile at a time. These characteristics are shown especially well in Fig. 3. Endameba buccalis. Showing differentiation of endosarc and successive, but single projections of pseudopods. Half second intervals. not extend long pseudopods, as this view would seem to indicate we would recognize that the apparent pseudopod is an erythrocyte and some adjoining foreign material. The apparent effect of this is that of a slowly extending pseudopod. The other common species is known as endameba Kartulisi, discovered by Kartulis (8) in Egypt, the morphology of which is distinctly different from the preceding when seen in its natural state, but which, according to the manner of its dying, may take on forms quite unnatural to it in life and which more closely resemble the endameba buccalis. tile protoplasm practically all in advance of the granular mass. Figure 5 shows an endameba of this species, starting out on a journey, as seen in the first picture in the upper left. You will note that the condition just spoken of clearly obtains. In the second picture, one-half second later, we see the granular mass flowing within the pseudopod. Unlike the species buccalis, just described, this variety continues its projection almost entirely in one direction, which gives us the effect of a repeatedly extended single pseudopod. It will be noted that at the time the granular mass |