cavity. The cavity will then assume 44 degs. Fahr., the difference within one-tenth of a minute being 128-44-84 degs. Fahrenheit-a change which in any organ whatever would produce a most violent inflammation, if such an organ should not be well accustomed to it, like the hands. Few persons would even escape a rheumatism in case the hand should be exposed to such changes. Now, what does such a derangement mean in a tooth? It means disease of the protoplasma-fibres, interruption of the circulation-necrosis; precisely what Dentists observe. Young teeth, which are still more dependent on circulation, will be affected more easily than old ones, where the fibres are fewer, and which resemble, in some respects, an inorganic structure. As this disease takes place all around a gold filling, we might expect a zone of white necrotic dentine under such fillings. Amalgam fillings have an effect similar to gold fillings, yet in far less degree, owing to their inferiority in heat-conducting power. For the comparison, I give specific heat and conducting power of the common fillings, from the most reliable observations and calculations: We therefore see that the thermal effect of a filling not only depends on the heat-conducting power, but also on its specific heat; so the more the latter approaches that of a tooth, the less is it liable to produce sudden changes. In this respect amalgam is almost 100 per cent. superior to gold. Specific heat will manifest itself by the speed of changes, while the heat-conducting power influences the intensity. The difference in the above example of a gold filling was 84 degs. Fahr., while under the same circumstance amalgam would only have produced First heating, 104 degs. Difference, 46 degs.; that is, the effect is only one half, at the most, of that of gold. As to the relative speed of changes, it may be said that gold produces this change in one tenth of a minute, amalgam in one quarter of a minute. These figures may vary in different persons, locations of cavities, size and form of cavities, yet the fact will remain that, other things being equal, amalgam fillings will produce only one half the change of temperature of gold fillings in twice the time, therefore with far less insult for the tissue. I think that Dentists have observed that the cavity under an amalgam is-almost without exception-sound, and formed by live tissue. We should consider very well the thermal insult of gold fillings in young teeth. Oxy-salts of zinc resemble dentine somewhat in their specific heat and conductive power. Calculation, as in the above example of a cavity, would give a difference of about 2 degs. Fahr., which is almost insignificant. They may, in this respect, be considered identical with dentine. Gutta percha might rather have an opposite effect. The cavity around it will be kept at a more uniform temperature than if it was dentine, yet the difference would be only about deg. Fahr. in the above example. I might enter into the effects of fillings when being used, as to their distributing and transmitting the pressure of mastication evenly, but it would lead too far. A third effect of fillings might be termed chemical. A filling may affect the substance of the teeth by affinities, or might protect it by neutralising the acid around it. In this respect gold is completely indifferent; it is not acted on by, nor does it act on, any liquid in the mouth. The filling is excellent, yet this excellency of the filling has its defect. It does not protect the tooth as oxy-salts do. Small cracks between tooth and filling are not filled up with oxidation and sulphurisation products. Tooth and filling are never cemented together. This inactivity of gold, therefore, is very dangerous for the tooth, though not for the filling. But what do we wish to preserve? It is quite different with amalgam. Though acted on but slowly by the liquids of the mouth, yet it is acted on suffi ciently to fill up small cracks between tooth and filling and to become cemented to the tooth. The filling becomes tight by the same principle by which steam-boilers are made tight. The boiler makers make the seams tight by oxidation, which they foster by certain mixtures. The rust fills up small cracks, so that a boiler of iron is far easier to make than one of silver or gold. With gold, in fact, it would almost be impossible to make a boiler, for this reason alone. -because no hammering can fill up cracks as perfectly as oxidation. Yet amalgams have another disadvantage-their shrinkage. The process of hardening of amalgams is one of crystallisation, due to the formation of chemical combination. We know but few cases of such combination where the volume of the combination is the sum of the volumes of the elements. Generally contraction follows, rarely expansion. Tin and mercury form the following compounds : Sn, Hg, with 34 per cent. mercury. Sn, Hg 46 دو The only compound without shrinkage is Sn Hg. Sn, Hg shrinks about 8 per cent. Theory gives, therefore, quickly the proportions of a good amalgam, supplanting years of planless trying. More than 75 per cent. of mercury cannot be combined chemically with tin. The excess will disappear in time, and cause a very great shrinkage. Similarly, with silver and mercury; many compounds are known with 64 per cent. Hg, 72 per cent. Hg, &c. All silver amalgams are very soft, shrink considerably, and lose relatively easily, their mercury. Still less stable are compounds of gold and platinum and mercury. The mercury evaporates from platinum as if no combination had taken place. The causes of shrinkage are therefore three :-Crystallisation, disappearance of mercury in excess, disappearance of "combined" mercury. I am at a loss to say why some amalgam makers put gold or platinum in their amalgams, if it is not to give to their amalgams some nice taking name-gold amalgam. How a certain mixture will work is very difficult to tell beforehand, yet we may always get an approximation to the truth. I will not deal here with the other objection-that mercury might "get into the system " from an amalgamit would show too much esteem for certain medical superstitions. The oxy-salts of zinc act chemically. While being put into the tooth the chloride of zinc or phosphate of alumina will decompose a small quantity of lime salts; but this action will cease as soon as the filling has hardened—that is, the chemical union, ZnO+ZnCl2=Zn2OCl2, has taken place, and the very small quantity of carbonic acid, &c., formed is very easily absorbed and the tooth not further molested, nay, it is now even actively protected. These fillings are more easily decomposed by acids than the tooth substance; hence they neutralise the acid near the tooth and thereby protect the tooth. As a necessity, they will disappear, and that is what the average patient alone observes. He cares less about disappearance of the tooth than of a filling! Much remains to be done everywhere in the line of education and fostering the work of doing one's own thinking. As oxy-phosphates resist far more-I made experiments on this point-than oxy-chlorides, they are to be preferred. The chemical effect of gutta percha might be an unknown physiological one, yet grossly chemical, it is inactive, though resisting less liquids in the mouth than oxy-salts, without protecting the tooth. Fillings sometimes produce phenomena of electricity. I do not mean anything in the line of the so-called new departure, which displays all the errors possible as far as electricity is concerned. I mean contact or statical electricity, affecting nothing but the nerves, but often most markedly. Also in this line gold fillings are the worst, because of the great potentiality of gold in electrical combination. Oxy-chlorides and gutta percha have no effect at all, and amalgam very little. By irritating the nerve constantly, as in a case of Dr. Stockwell's, where an amalgam filling was capped with gold, they may produce persistent neuralgia, and perhaps physiologically, produce changes in the nutrition of a tooth. Yet, as the unpleasantness is very great, we will avoid it. It is unnecessary to say that only the contact of two metals produces such electricity, like a gold filling and a spoon or fork, &c. I would sum up my conclusions thus: Gold is the worst filling in most cases. It should be used chiefly in old teeth. Amalgams should be used everywhere where the patient's fancies, notions, and similar kinds of bias do not prevent it; while oxy-salts of zinc are the fillings for frail teeth, for capping pulps, &c. Yet let Dentists never forget that none of them is the ideal filling. This is not a metal, it is a silicate, translucent like the tooth, not acted on by acids, capable of a high finish-in short, a filling resembling the tooth-substance as closely as possible. Let not the foggy dogma of the superiority of gold act on progress as the old mediæval superstitions acted on astronomy, physiology, and zoology for so long a time. Because gold is so much life's only aim with most people, they forget that gold has no intrinsic claim to its superiority except long-sanctioned custom; that chemically it is far inferior to platinum, mechanically to iron, and still more to steel; that its colour is not finer than that of brass. Unclear alchemistic ideas are still active everywhere. They are the worst obstacle to clear logical thoughts. The Dentist has to educate people, yet first he himself must not be biased by the same scientific superstitions. Let him never get tired of searching for something better. We shall never reach perfection, and the field of researches is as boundless as space and time. So far the views of the theory-only the practical Dentist can judge how far they are in accordance with his experience.Johnston's Dental Miscellany. Hospital Reports and Case-Book. ABSCESS IN THE MOUTH CONNECTED WITH BARE By HENRY MORRIS, F.R.C.S,, ON November 11th, 1880, Ellen W-, aged 26, a weakly, very anæmic, and pale-looking blonde, who all her life has had bad health, was admitted into Regent Ward of the Middlesex Hospital with an ovoid swelling the size of a large walnut in the roof of the mouth, projecting downwards toward the tongue. It was situated chiefly on the right of the median line, and fluctuated and discharged daily a small quantity of rather offensive matter into the nose as well as into the mouth. Her jaws were filled with the decayed, ragged, and offensive stumps of molar and bicuspid teeth. The swelling in the mouth appeared three weeks before admission, and was attributed to the irritation caused by the first right upper bicuspid tooth, which had been for a long time carious, and had decayed away, leaving only a stump. This stump was extracted nine days before admission. A fortnight before coming in the swelling on the palate was lanced by the patient's regular medical attendant, and a quantity of blood and matter came away. It filled again in three or four days, and subsequently broke of itself, and discharged in two places-one where lanced, and one just behind the front teeth. A week before admission the discharge into the nose began. The mouth was slightly examined on the day of admission, but owing to her weak state of health and her fainting under examination, nothing was done until the next day (November 12th), when a free antero-posterior incision was made into the abscess, and two or three drachms of mixed blood and pus evacuated. With a probe the whole palate process of the right maxilla was felt bare and rough, and the probe passed through a carious |