Changes in Caudal Bones of the Rat as an Index of Ossification. ∗

The conventional method of determining the rachitic condition of a rat by either the X-ray or the “line test” method has been restricted primarily to an examination of the longer bones of the rat's body, especially the proximal end of the tibia or distal end of the femur. While a study of the structural changes in such bones furnishes a reliable index of the degree of rickets manifested by the animal in question, a comparison of X-ray photographs of the whole body of such animals indicated that other bones of the skeletal framework might offer some advantages over the tibia and the femur in this respect. This appeared to be especially true of the bones of the tail. This particular body structure appeared to offer a series of provisional zones of calcification which could be studied by either the X-ray or the “line test” method. In fact the tail of the rat had been found to be both more easily and more effectively X-rayed than was the leg and, in addition, it afforded possibilities of removing portions of the bony segments for “line test” during the course of the experimental period, without serious consequence to the health and well-being of the experimental animal.

In connection with another investigation being carried out in this laboratory in which a large number of rachitic animals were being-involved, a comparison was made of the X-ray and the “line test” findings, where both the tibia and the caudal bones were considered. A general idea of the comparative results obtained may be had by observing Plates 1 and 2, which were obtained from X-rays and “line test” photographs of the bones of 6 typical animals that represented various stages of ossification.