DR. REILLY:—I think I was cautious about that statement. I said, to all appearances, it had not decayed. Of course, I could not tell absolutely, only from my experience in excavating I judged it was about the same as when I first saw it, perhaps a little harder. If we were not able to judge something of the depth of decayed dentine, we would be in constant danger of exposing the pulp. If you cannot tell by the feeling of your excavator when you are near the pulp, I would like to know what you are going to do in those cases where you cannot see the bottom of the cavity? DR. SMITH:—Yes; but you say you did not use your excavator in this case. DR. REILLY:—I reached my conclusions while wiping out the cavity with the forceps and cotton, and I thought then, and it is my feelings now, that decay had not gone on in that cavity at all. I think it is possible for such a condition of affairs to exist; I think that things stand still in such a condition. I had a case the day before yesterday which was treated some ten years ago, and on removing the filling I found the pulp canals filled with cotton. There was no odor at all—perhaps the cotton was slightly discolored, but the cavity was in apparently the same condition in which it had been left; and it seems to me that if a tooth would remain in that condition with cotton, why wouldn't it be preserved under gutta-percha in just the same condition? I don't know why the gentleman should conclude that it would decay? What leads him to think that it would decay? DR. SMITH:—I don't know that it is so, but I have read somewhere that in decayed dentine there exists "pesky little bugs," and if a cavity is stopped up and these micrococci, or bacteria, cannot get at the oxygen which comes to a cavity from the outside, they will work in to the dentine and decalcify the tooth substance in the search for that food which they live on. It is not my theory, but I read it somewhere, and in my practice I either kill the bugs or take them out. DR. REILLY:—That theory may be all right, but it does not work out in my practice. The experience that I had with this young man has been repeated over and over. I do not excavate carious dentine as far as it can be, and I don't think that theory will work out in all cases. If bacteria are there after the cavity has been thoroughly cleansed and tightly stopped, they must find an early death in some way.