mation of calculus. And if this consolidation is produced by the saliva, then the amount and completeness of the enamel hardening will be in direct relation to the nature and composition of the saliva. This then leads us to a consideration of the saliva in quest of the properties which are responsible for this calcifying process upon the teeth. We accordingly, in the pursuit of this problem, have turned our attention to a study of the saliva in its relation to the character of the enamel surfaces and susceptibility to dental caries. In our search for this variable among the inorganic constituents of the saliva we made quantitative estimations of the total ash. The results so obtained were disappointing as there appeared to be no correlation between the variation of total ash in the salivas examined and the condition of the teeth. When, however, we made quantitative estimations of the calcium content of the various salivas the results obtained had a more significant variation and gave promise of being worthy of careful consideration.

Inasmuch as the total amounts of calcium to be found in samples which were easily obtainable were exceedingly small, and as this calcium was mixt with a large number of other substances which are commonly found in the saliva, it was necessary that the method of the determination be very carefully worked out in order that the results obtained might be reliable. After very thoro trial the following technic was adopted as the method by which all our determinations should be made: 25 ccm. samples of saliva were dried down in platinum crucibles over a sand bath. The residue was converted into the oxides by heat and burned until they turned to a white powder. This residue was then taken up with dilute acetic acid, brought to a boiling temperature and precipitated with hot ammonium oxalate. This solution was allowed to stand for several hours and then filtered. The precipitate

was then washed, dried, and again converted to the oxide of calcium by heat in a platinum crucible, in which form it was weighed. All data on calcium determinations are given in the form of CaO obtained from 25 ccm. of saliva. CALCIUM DETERMINATION IN THE SALIVA.

Our estimations of calcium were made on the following classes of cases; students who appeared to be continuously immune to dental caries, students who were plainly susceptible and others who were indeterminate, women in the maternity ward of the hospital, negroes, and children. In every case an effort was made to check up the appearance of the enamel surfaces, as to color, density, and opalescence, with the calcium content of the saliva. We found that the various salivas gave readings which ranged from .0015 mgm. to .0040 mgm CaO per 25 ccm. of saliva. These readings remained fairly constant for each individual in tests extending over several months and did not vary materially when taken at different times of the day. All samples collected were of the whole saliva by means of chewing paraffin.

In eight characteristic cases of distinct caries immunity the readings were as follows:

.0035 mgm Ca0 in 25 ccm. of saliva

The salivas of over 50 women in the maternity hospital were examined at various stages of pregnancy, some of which were re-examined at intervals up to the time of their delivery. The data so obtained showed that the calcium salt content of these cases varied over a wide range, from .0015 mgm to .0035 mgm CaO in 25 ccm. but on the whole they were decidedly lower than individuals of the same age. We found that many of these cases in which there was a low calcium content, also had a large number of cavities and a peculiar whitish to blue-white appearance of the teeth. In many cases the tips of the incisors and labial and buccal surfaces were turned to a white chalky condition. It was also noted that as these patients advanced in pregnancy the saliva decreased in calcium. This decrease became very marked at the eighth month when the calcium fell to .0015 mgm and .0017 mgm CaO per 25 ccm. There was some exception to this as several cases, especially among the negroes, remained high thruout their period of pregnancy. These cases all had yellow, dense appearing, enamel and were seemingly not susceptible to caries.

Results obtained from the examination of the salivas of a number of children were surprisingly high as none were found which ran very low while many were exceptionally high. The readings in 5 such cases were as follows:

E. L. Age 11 .0032 mgm CaO in 25 cem. of saliva 5 .0037

F. B. C. S. C. Y. P. F.

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In our correlation of the calcium content of the saliva to the condition of the enamel surfaces we were forced to rely upon observation and the presence or absence of new cavities in the teeth. It was our experience, however, that whenever the content was high the enamel surfaces had a more dense and opalescent appearance with every indication of surface condensation. While in many of the cases in which the calcium was low the teeth were white or blue-white in color and had the appearance of roughness and permeability. So noticeable was this fact that we could roughly estimate the amount of calcium in the saliva of many individuals by the color and appearance of their teeth. A further correlation may be seen in the fact that implanted teeth and natural teeth used in bridge work, altho they may be quite different in color at the time of insertion, frequently change to the shade of the adjacent teeth. Since the nutrition of these teeth has been entirely cut off, this change in color and appearance can only be attributed to the influence of the saliva in which they are bathed.

In a consideration of the calcium content of the saliva in its relation to the health of the teeth there are two forms of action which should be considered. One, that of the possible part which it plays in the consolidation of the external surface of the enamel, thereby making the tooth less pervious to moisture and organisms and rendering the surface of the enamel more self cleansing. The second is the ability which a high calcium content in the saliva should exert in neutralizing acids formed in fermentation of carbohydrates, thus inhibiting their action upon the.tooth in the production of incipient caries. This latter view was stated at some length by Dr. F. W. Broderick of London in a paper entitled "Calcium Metabolism and Dental Caries" which was given before the VIth International Dental Congress. He regards calcium in the form of bicarbonate

as the chief source of salivary alkalinity and its presence or absence he regards as a direct influence upon the process of caries because of its antacid properties. He discusses calcium metabolism in the body and the effect of the various internal secretions upon it, and states as his belief that the calcium content of the blood and the saliva is lowered during the stress periods of life thereby favoring the process of caries of the teeth. He claims to have raised the calcium index of the saliva by injections of a poly-gland substance composed of suprarenal, pituitary, and thyroid extracts. He concludes that "the predisposing cause of dental caries is a diminution of the calcium utilizing power of the body, due to a want of balance in the secretions of all the ductless glands brought about by any pathological condition causing extra stain to be thrown upon them."

These views which have just been stated are interesting as a correlation of our calcium study, but at the present time we do not feel justified in giving assent to the statement that "the predisposing cause of dental caries is a diminution of the calcium" in the sense that it is the all predominating influence in determining the process. We believe that there are many other factors which enter into practically every case of caries, of which the calcium of the saliva is but one. And yet we feel that the calcium in its relation to the surface of the enamel of the teeth, and in its power of neutralizing the acids of fermentation, is a very important factor in the process, which by its action may in many cases be able to swing the balance of forces toward immunity on the one hand or susceptibility on the other.

EXPERIMENTS ON ENAMEL
SURFACES.

In a further study of this problem we attempted to produce consolidating changes in the enamel of teeth in the test tube under conditions somewhat comparable to those found in the mouth.

With this in view, three extracted, unerupted third molars were split in half axially. One-half of each was placed in a test tube and given to three students whose salivas were high in calcium salt content. The students were instructed to cover the tooth with their own saliva and change same several times daily. These teeth were carried in this manner for 30 days, at the end of which time the three half teeth, together with their corresponding halves which were kept for control, were treated with silver nitrate in the following manner. The teeth were immersed in a 10% silver nitrate solution and subjected to reduced atmospheric pressure under an exhaust pump. The air was allowed to enter occasionally and again pumped out, which process was continued for about two hours, at the end of which time the teeth were taken out and placed in the direct sunlight for several hours. They were then sectioned and mounted for examination. In each of these cases, there was plainly seen in the original sections a marked difference in the penetration of the silver nitrate in the two halves, it being considerably less in the halves which had been carried in the high calcium salivas. An attempt was made to photograph the sections thus obtained. Figs. 1 and 2 are taken from one of the sets just described, Fig. 1 being the half which was carried in the saliva and Fig. 2 the control which had not been so treated. The partial filling up of the canals in the periphrey of the enamel which had been accomplished in the short duration of the experiment could only be attributed to an action of the saliva, as all nutritional processes had stopt.

In a comparison of the various types of teeth a number were selected which had polished and dense appearing enamels, and others which had a softer and less dense appearance. These were subjected to silver nitrate and in each case the penetration of the dense appearing enamels was less than of those which did not ap