Abstract
These results are based on a study of 150 rats, taken from the mothers at the age of three weeks when they weighed about 30 gm. and placed on experimental diets in small separate cages shielded from ultraviolet rays of sunlight. They were not given cod-liver oil or butter fat, but they had sufficient vitamine-A for varying degrees of growth. All of them were x-rayed at the end of this period and turned over to Dr. C. M. Jackson for morphological study. His observations have confirmed my diagnoses.
In order to diagnose rickets in rats the average P metabolism and growth per day were determined (weights being expressed in milligrams) and the following empirical formula was used. Rachitic index = RI.
RI = increase in body weight × 0.0022 − (P retention − 2).
If RI is positive the rat has rickets and if negative the rat is normal. For example, if a rat increases in weight 2,000 mg. per day, 2,000 × 0.0022 = 4.4. If its P retention is 4 mg. per day, 4 − 2 = 2 and RI = 4.4 − 2 = 2.4, therefore, this rat has rickets. If the P retention is 7 mg. RI = − 0.6 and this rat is normal The magnitude of RI, if it is positive, denotes the severity of rickets provided the metabolism has been determined over long enough periods and with sufficient accuracy, but the skeleton grows on a “maintenance” diet and this tends to disturb the applicability of the formula. Rats usually retain 1/5 to 1/3 of the P of the diet. Since a rat's body contains about 0.5 per cent. P and the normal rate of growth is about 2 grams per day they should retain about 10 mg. P per day or 5 mg. per gm. increase in body weight, and this is found in normal rats of the age studied.
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