their invisibility. Burmese rubies are transparent; imitation rubies opaque. This may foreshadow their usefulness in the jeweler's art. By far their most useful and practical application is being made in the field of surgery. To photograph the hand place it on the plate holder, remove rings from fingers; for the foot, place it on the floor, remove shoes which contain iron nails; in case of the trunk the patient lies upon the plate-holder; in case of the skull the head is strapped to the plate-holder because of the long exposure required. Time of exposure varies with the size of coil, voltage of primary current, size of tube and the degree of vacuum. With perfect apparatus the hand and foot require from two to five minutes exposure ten to fifteen inches distant. As the rays proceed in straight lines it is difficult to skiagraph extensive surfaces. Possible applications may be skiagraphing bones or detection of foreign bodies, as needles; recognizing irregularities, deformities, new growths, malformations, fractures, dislocations, variation in density of bone etc. It is possible to locate mineral matter in arteries, bladder, kidneys and note progress of ossifications in children; for the dentist to locate roots of teeth, foreign bodies, suspected fillings, supernumerary or non-erupted teeth, viewing the antrum, etc. It is also possible to locate the viscera and note the movements. Such are the possibilities opened up to science by the X-Rays; making possible in one sense, the fulfilling of the poets' aphorism: that the proper study of man is

man.

Scientific discoveries are based upon those that have gone before. Beyond doubt there are other rays in the universe. As there are sounds our ears have never heard, so there is light our eyes have never seen.

For not by visible light alone,

Where God has built his blazing throne,

Nor yet alone in earth below,

With belted seas that come and go

And endless isles of sunlit green,

Is all our Makers glory seen.

Year after year our knowledge is increased; ignorance rolled further and further back; where now there is darkness there will be light.

The Preparation of a Cavity and Insertion of a Gold Filling in the Distal and Occlusal Portion of a Second Lower Bicuspid.

BY F. E. RENKENBERGER '99.

The preparation of a cavity in the distal surface of a second lower bicuspid, for the retention of gold, is a very essential part of the operation.

If the cavity is very large it can first be roughly excavated before the rubber dam is adjusted. The rubber dam being applied the cavity is thoroughly dried with hot air, which will aid the operator to distinguish between the living and dead tissues. All decay being removed the cavity is properly formed for the retention of gold. If the teeth are very close together it is necessary to separate them before filling. This can be done in several ways.

Some operators prefer the slow method, by the use of a twist of cotton or a soft piece of wood. Others use a separator. The use of the latter depends on the condition of the patient. If the patient is very nervous it is better to apply the first mentioned method, as less pain is occasioned by it, or if the walls are frail a saw may be used to secure enough space for the matrix.

Space being attained, all decay should be removed. When the carious cavity has been such that the bottom is smaller than the orifice, small pits may be drilled into the walls of dentine to make retaining form for the filling. The orifice should always be a little smaller than the bottom of the cavity to retain the filling. The bottom of the cavity should not be rounded, but rather flat, so that the first piece of gold will wedge firmly to the walls of the cavity. Care should be taken not to make the cervical border too frail, as it will be liable to break and leakage will follow. This seems to be the vulnerable point and great care should be exercised to make a perfect union between the gold and walls of the cavity.

If the gum should extend into the cavity, it is well to pack it over full with gutta percha for several days. This will push the gum out so a matrix can easily be applied.

The occlusal surface should be carefully excavated, if the cavity is very deep the walls should be nearly parallel. The occlusal portion of the cavity may be wedge shaped, or may

have a small groove cut on buccal and lingual walls where they join the anterior margin. This will form a wedge shaped space and hold the filling firmly. The enamel on the occlusal surface can best be cut with a sharp chisel or fissure bur. If the cavity is very shallow a slight groove may be cut along the edge of the enamel and dentine which aids in the retention of the filling.

In

The cavity now being prepared and properly formed, it is well to apply a matrix to form the distal wall of the cavity. Matrices are of various kinds. If the space acquired is large enough, a band matrix may be used to good advantage. If the space is rather narrow a common steel matrix may be used. applying the matrix great care should be taken to fit it to the contour of the tooth, and have the cervical portion well wedged against the border of the cavity. This can be done by a separator or by an orange wood wedge dipped in sandarac varnish and applied against the matrix and adjoining tooth. Oxyphosphate of zinc may also be used which will rapidly set and hold the matrix in position.

The cavity being properly prepared, disinfect and thoroughly dry with hot air. Apply your first piece of unannealed gold. Be sure you have it large enough to come out flush with the cervical margin of the cavity, condense thoroughly and continue until the cavity is filled. Crystal gold may be used to start the filling and finish with gold foil. It is claimed by some authors that it packs more tightly to the walls of the cavity. But Dr. Watling says "No," as it is impossible to condense so many fine granules into a solid mass as easily as the thin gold foil.

Care must be taken not to bring the plugger in contact with the walls of the cavity, as the walls are easily fractured, which may cause decay to follow. Fill the cavity flush and be sure you condense every piece of gold and especially the occlusal surface. Remove the matrix and then polish the filling, using the disk or strips on approximal surfaces. Grind the occlusal surface with the gold finishing burs followed by the corundum. wheel and wood points and finish with the burnisher.

The paper just presented is a difficult one to discuss. He has treated the subject in such a manner as to leave little to add and less to criticise.

One point to which I take exception is the drilling retaining pits into the dentine. My objection to this is based on the well known fact that, when the filling expands and contracts under the influence of the thermal changes, the main body of the filling will break away from these small points and thus become loosened.

Another method of preparing this cavity, which I think deserves our notice, is the one now in use in the Chicago school. It consists of cutting away the disto-labial and disto-lingual angles of the tooth, thus bringing the lateral margins of the filling away from the proximal surface, and onto a part of the tooth that is, in a measure, self-cleaning. By this procedure, the liability to decay starting at the lateral margins is greatly lessened. In such a cavity the filling is retained by a form at the cervical portion and another on the occlusal surface. The latter is called a "step" form. The fault to be found with such a cavity is the fact that it does not lessen the liability of decay recurring at the cervical margin which, the writer truly says, is the most vulnerable point.

Another feature, which the writer did not mention, is the filling of this cavity when the first molar has been extracted for some time and the bicuspid tipped backward. These conditions. greatly add to the difficulty of filling the cavity. In this case Dr. Hall dispenses with the matrix and uses the tin pluggers with hand pressure. As for myself, I prefer to use a band matrix and the mallet as I am firmly convinced that better adaptation and more thorough condensation can be secured by the use of the mallet than by hand pressure.

In conclusion I would say that Dr. Watling is authority for the statement that, as a rule, better fillings can be made, in such cases, with amalgam than with gold.

Predisposing and Accidental Causes of Dental Caries.

BY C. G. MESEROLL, '99.

We may divide the causes of dental caries into three classes, viz: predisposing, accidental and exciting. The first two, which for the sake of convenience, are often given under the one head, predisposing.

The most important, perhaps, of the predisposing causes is defective form, which is congenital and often hereditary, and is most commonly manifested in the form of pits and fisures, principally upon the molars and bicuspids. The pits and fissures are caused by improper development of the enamel organ during the process of tooth formation, and may be superficial or deep, sometimes extending nearly or quite through the enamel, leaving the dentine unprotected, or nearly so, and affording every chance for the lodgment and fermentation of food particles.

The dentine itself may be weakened by the presence of interglobular spaces, which, if at all extensive, form excellent pathways for the progress of decay. Even if small they lessen the resistance of the dentine to decay.

The teeth may be defficient in structural qualities, in quantity and quality of lime salts, resulting in soft, chalky dentine and frail enamel, easily disintegrated by the agents of decay. These conditions are sometimes hereditary but may often be bettered by intelligent and systematic care of the body, proper kinds of food and healthy exercise. Lack of vital tone in the individual renders any organ of the body an easy prey to disease, and the teeth are no exception to this rule. They must have a sufficient amount of nourishment or they will be unable to successfully resist the action of the acids and bacteria of the mouth. This is shown by the frequent and very rapid progress of caries in the teeth of pregnant women.

The fluids of the mouth are often vitiated as a result of lowered vitality of the general system, or of a specific disease, as dyspepsia. Some writers claim that severe fevers are especially active as predisposing causes of caries. Of course they lower the vitality of the body very greatly, and cause more or less neglect of the teeth, as do other diseases.

Certain diseases of childhood, occurring at or just before the time of eruption sometimes seem to injure the teeth to a greater or less extent, often discoloring and softening the enamel.

Another prominent predisposing cause is malposition of the teeth. When they are correctly arranged in the arch, they have very small points of contact and normal approximate spaces and are therefore nearly self-cleansing. But if they are