Tensile Strength of Tibiae of Healed Rachitic and Normal Rats. ∗

Abstract

The early observation of Clark and Mrgudich 1 that rachitic and healed rachitic rat tibiae had lost the preferred longitudinal orientation of the crystal micelles of the inorganic material prompted investigation of the tensile strength of healed rachitic bone as compared with normal controls. Albino rats from the stock colony were used. At weaning, 5 litters, comprising 30 rats were divided equally into control and experimental groups. The control animals were kept on the stock diet, while the experimental group was placed on the Steenbock-Black rachitogenic diet. After 41 days the experimental animals were severely rachitic, as shown by X-ray photographs. They were then given 250 units of calciferol by mouth and placed on the stock diet. Prompt healing of the rickets resulted. The animals were continued on the stock diet for 6 weeks after the calciferol was fed, and at the end of this time no roentgenological difference could be demonstrated between the experimental animals and their littermate controls. The rats were killed by a blow on the head and the tibiae immediately removed and dissected free from soft tissues for determination of tensile strength.

The apparatus used is a modification of a standard engineering machine for testing structural material.† The tibia is supported on 2 blunt wedges 10 mm apart, and a blunted knife edge is placed on the bone from above to apply pressure. By means of a motor and suitable reducing gear a heavy weight is slowly pulled across the apparatus so as to increase the pressure on the bone through the knife edge. A writing point records the excursion of the weight, so that the total load on the bone at any instant may be calculated.