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PYORRIKKA ALVEOLARIS. 17 1.16. In the same volume, the analysis of human saliva by Bidder and Schmidt, in 1,000 parts, shows one item of 0.98 composed of sodium, calcium and magnesium phosphates. From the preceding analyses, it is evident that the propor- A f tion of lime salts in pus is far in excess of that in saliva at any point of production, singly or mixed. With these facts in view, it should be rather a matter of surprise that the deposition of calculus within these " pockets " continues so small. MECHANICAL CONSIDERATIONS. — In response to a proper instrument properly applied—the invisible calculus may be brought away, but always in small particles: never in liberal masses like ordinary salivary calculus. Should the root be affected upon a side that is flattened or grooved, the crustation will extend along the flat or in the groove, and in some cases approaches the apex ; but if the surface be convex, the calculus frequently may be found crossing horizontally, feeling to the operator like a ligature of small, hard cord or wire ; this latter form is always near the cervix, and easily removed. The absolute and complete removal of the concealed incrus- tation should be the operator's first and chief solicitude, as failure in any part of this procedure insures failure to effect a cure. Sometimes, but fortunately not always or often, this con- 2