Data on calcium and phosphorus1 of the serums of 250 healthy children from 5 to 16 years of age were analyzed in an investigation of dental caries.2 This gave us an opportunity of studying the physiologic relation of these substances to such factors as age, sex and development and their physiologic variation.
METHODS
After the children had rested for at least fifteen minutes, blood was withdrawn with as little stasis as possible. It was not collected under oil. As soon as the blood clotted, the specimens were centrifugated, and the serum was separated from them. All determinations were made immediately after the collection of the blood. Duplicates for calcium were done, except in a few cases.Calcium.—A modification of the Clark-Collip method,3 involving the adjustment of the ph to about 5, and two washings of the precipitate were used. The average deviation of duplicates was 0.25