At the International Medical Congress, held in London in 1881, Drs. Underwood and Milles produced a joint paper, in which they attributed caries of the teeth to the direct action of micro-organisms which, penetrating the dentinal tubuli, destroyed the living substance of the tooth, leaving the inorganic matter to be broken down and washed away in the fluids of the mouth. This theory was accepted by many persons in this country, and is still vehemently urged by them.

In the laboratory of Carl Heitzmann, of New York, observations were conducted by him, and by Drs. Frank Abbott and C. F. W. Bödecker, and their conclusions were published to the world. Their theories necessarily rested upon the reticulated structure of protoplasm, as taught by Prof. Heitzmann. They held that caries was essentially due to an inflammatory condition of this reticulated vital matter, and that the course of the discase did not very materially differ from that of inflammation in other tissues.

In 1881, at Wiesbaden, in Germany, at a meeting of the American Dental Society of Europe, some of those present listened to a paper by a young dentist previously unknown to fame, except as the thoroughly educated son-in-law and coadjutor of the well-known Dr. F. P. Abbot, of Berlin. This was the first of a long series of papers since published by Dr. W. D. Miller, and it was the initial point of a course of experiments and observations such as were new to the history of dentistry. The results are before the profession, and they have placed their author in the very front rank of experimental observers. He proceeded scientifically and systematically to make an exhaustive study of his subject by cutting thousands of slides of diseased teeth. In these he found micro-organisms invariably present, so that he was enabled to deduce the rule that they were in some way essentially connected with caries of the teeth. Thus far Milles and Underwood had proceeded, and to this point his observations were corroborative of theirs. But he proceeded further, and endeavored to determine in just what way they were instrumental. He made pure cultures of these organisms and studied their life-history. He segregated a number of them, and was thus enabled to study them morphologically, physiologically, and chemically. He pursued these investigations perseveringly and unweariedly. On his late visit to this country he brought with him some of his pure cultures, and I have the pleasure of exhibiting a few of them to you now. It should be remembered that within these little tubes is contained the record of the most exhausting work, continued un

remittingly for three years. So great was the difficulty that attended their production that it was a full year before he was able to segregate a single one of these organisms successfully.

He has demonstrated that caries of enamel is produced almost, if not entirely, by acids generated in the mouth; that caries of the dentine is largely, if not wholly, due to the action of micro-organisms, or ferments, that secrete or produce within the dentinal tubuli an acid that has the power to decalcify tooth-structure, and thus caries penetrates deeper and yet deeper within the body of the tooth, the decalcifying process preceding the actual presence of the organisms. By inoculating a culture fluid, or medium, with a certain definite organism, in an acid or neutral solution, he has succeeded in producing artificial caries that it is impossible to distinguish from that which occurs in the mouth. It is, possibly, unfortunate for him that he has not been fully comprehended by those who did not perceive the difference between putrefactive and fermentative organisms. It is only the latter that are active in the work of caries.

Perhaps I cannot better summarize the results that he has obtained than in his own words, at the close of his series of articles in the Independent Practitioner, July, 1884:

1. I convinced myself by the examination of some thousands of slides of carious dentine that micro-organisms were always present, and that they, without any doubt, were the cause of various anatomical changes which were found to take place in the structure of the dentine during caries. Of course, the question of priority does not suggest itself; Leber and Rottenstein, as is well known, were the first to give definite expression to this fact.

2. I proved, at the same time, that the invasion of the micro-organisms was not, in the majority of cases, simultaneous with the softening of the dentine, but that large areas of softened dentine could be found that contained no fungi. Of all those who examined my preparations in America, no one, whatever his theory, ever once denied this fact. I concluded from this that the softening of the dentine went in advance of the invasion of the organisms.

3. I determined, by analyses of masses of carious dentine sufficiently large to give reliable results, that the softening of the dentine is of the nature of a true decalcification; that the decalcification of the outer layers is almost complete, and diminishes in degree as we advance towards the normal dentine; furthermore, that the same relations maintain in dentine softened in a mixture of saliva and bread, or in weak organic acids; also, that in a mass of carious dentine the lime-salts had been removed to a much greater extent than the organic

matter.

4. I maintained from the first that the softening of the dentine was produced by acids, for the most part generated in the mouth by fermentation. I had, however, no direct proof of this.

5. I proved that fungi exist in great numbers in the human saliva and in carious dentine, which have the power to produce acid under conditions which are constantly present in the human mouth. I determined this acid, for one of the fungi, at least, to be the ordinary ferment, lactic acid.

6. I produced caries artificially, which under the microscope cannot be distinguished from natural caries, by subjecting sound dentine to the action of these fungi in fermentable solutions.

7. I determined the influence of various antiseptics and filling-materials upon the fungi of caries.

8. I isolated various forms of these fungi, and determined in part the conditions most favorable to their development, their characteristic reaction upon gelatine, their physiological action, their effect when inoculated into the system of lower animals, and their possible connection with certain obscure diseases generally attributed to the carelessness of the dentist.

At the late meeting of the American Medical Association, held in Washington, May, 1884, before the Section of Dental and Oral Surgery, Dr. G. V. Black, of Jacksonville, Ill., a man whom we all honor, read a paper that presents some novel views of caries of the teeth. I have not seen the paper in full, and am not therefore prepared to give an intelligent résumé of his theories and deductions, but I am assured that he will shortly present to the world a work upon dental pathology, and for that every thinking man of the profession will look with interest and eagerness.

In conclusion, I desire to say that, while wonderful progress has been made during the past year, the task is far from being completed. Dr. Miller himself says that there are yet, in his opinion, many factors that have not been intelligently or exhaustively considered. He himself will shortly commence a new series of observations and experiments, for which his previous labors admirably fit him, and from which his profession and the world of science have much to hope. Other students, in various parts of the world, are engaged in careful study, and we may well believe that we have entered upon an era that will end in the acquisition of knowledge that will enable us more successfully to cope with the difficulties of dental practice.

DISCUSSIONS.

Dr. SPALDING: I would like to inquire whether Dr. Miller has made any pure cultures from the dental caries artificially produced? Dr. BARRETT: That would be a work of supererogation. He produces dental caries from a single segregated pure culture, showing that there is one organism that produces caries.

Prof. MAYR: It seems to me that the apparent difference between the views of Dr. Miller and those of some of the first defenders of the septic theory in this country has been much exaggerated, thereby causing many to consider the whole subject as more doubtful than it is. This difference depends entirely upon what we call decay. You look into the mouth of the patient who complains of a decayed tooth. There is the smell of decay, there is pain. Now, the smell is not the decay, and the pain is not the decay. You take an instrument and dig around a little. After you have removed the outer mass of decayed matter, I do not think you have yet touched the point of disease. You must go down deeper. After you have excavated deeper, the patient begins to twitch. Now, I presume you have reached the point where you can begin properly to say that you have touched the decay. You excavate further, and the patient becomes happy again. It seems to me that in doing that you have gone through the decay; the decay was something between the mass which was first encountered and the healthy tissue of the tooth. I think all our dispute is because we fail to realize this precise point. The outer mass found in the cavity is not decay ; we agree on that. And, when we get through to the healthy tooth again, we recognize that this is not decay; but there seems to be a dispute as to the intermediate point. What is this intermediate point? Is it merely decalcified dentine that we meet with in that particular spot?

Dr. ATKINSON: Do you mean decalcified or dissolved?

Prof. MAYR I say decalcified, because almost everybody speaks in this way. Is this really decalcified dentine? is it simply a different form of the tooth, or is it an entirely new production? The real line of disease is probably not a thousandth of an inch thick ; the real diseased layer can certainly be fixed within a microscopically small territory: and we will never agree if we do not establish exactly our fighting ground. It seems to me that this is the only point of difference. Dr. Miller seems to me to be talking and experimenting altogether too much about the outer mass found in the cavity. This is of no particular interest; it is the corpse of a tooth. The point of interest is the thin layer where the physiological changes are going on.

We in this country have been experimenting and working, too, upon this subject, as well as Dr. Miller, although perhaps not with the same facilities. Dr. Miller has the one hundred professors, the fine microscopes, etc., of the University at Berlin at his disposal,

but I think some of the honor for what has been accomplished should remain in this country. I think it would be unfair to those who have labored in this country to so completely overshadow and silence them as it seems to me has been attempted. I do not say this for any personal reason, for I have no possible personal interest in it. A number of experiments have been made by investigators in this country, and, as I said before, the only point of difference between them and Dr. Miller seems to be in what each conceives decay to be. About three years ago, also, I made careful analyses of this diseased layer between the corpse or outer mass of débris and the healthy dentine. I was very careful in my work, and, though I had taken a mass of decaying matter which was only one seventeenth of a grain in weight, I was sure of my results; and in this thin layer there was no diminution of the lime-salts. There was no doubt about it. Therefore, whatever may be true of the outer mass, as to that particular layer about which we are fighting, I have a conviction, and an honest conviction, based upon my personal investi. gations, that, at the real point of decay, there is no appreciable loss of the lime-salts. The process of decay at this point is a physiological process, some may say a pathological process; but that depends only on the view you take, for physiology and pathology comprise the same processes, only the first are in our favor and the latter against us: hence a subjective difference of no value. This process is, to my conception, a physiological one, and, therefore, to say that we have settled it by saying decay is due to fermentation from without seems to me to be very reckless. I would rather say that this precise phenomenon which we call the process of decay is still in the realm of physiological processes, and is not yet definitely settled.

Dr. ATKINSON: I rejoice with exceeding great joy that we have at last come to a point, and that point is the initiation of the action that is nominated decay. Where does that occur? We have just heard from my learned and beloved friend. He said one word that, were it written in deep lineaments upon all our consciousness, would be a talisman to deliver us from all evil of investigation. That is, to have one definition, one term expressive of one process, and then we would not be so tangled up, and have to deal so ambiguously with questions that clearly come before the mind, but that cannot be brought to be revealed to the senses. The products of a process, as the last speaker has learnedly and clearly shown, are not the process itself. The tracks of the game would make a poor dinner.