The MacLagan Penetrometer (ca. 1910-1915)

The MacLagan Penetrometer (ca. 1910-1915)

Penetrometers are used to determine the optimal exposure settings for performing an X-ray of a particular part of the body.  They typically consist of a series of metal (usually aluminum) plates of increasing thickness. Sometimes they are arranged in the form of stair steps.

The MacLagan Penetrometer (ca. 1910-1915)
The MacLagan Penetrometer (ca. 1910-1915)

This particular unit, the MacLagan Penetrometer, was manufactured by the McIntosh Electrical Company, or as it was later known, the McIntosh Battery and Optical Company of Chicago. I am not sure when the firm changed its name, other than that it was done by 1912. McIntosh seems to have gotten into the X-ray business by producing static high voltage machines. The Hogan Silent XRay Transformer, referred to on the plate (below left), was a featured product in their 1912 catalog.

The MacLagan Penetrometer (ca. 1910-1915)

The penetrometer contains ten metal disks arranged on the inside like the numbers of a clock, and each disk has a number cut through it so that it shows up on an X-ray image (photo above right). According to the plate, the number indicates that a particular disk corresponds to so many inches of solid tissue. As such, the images of the various disks on a test X-ray would indicate the appearance of body parts that correspond to the indicated thickness.

The above advertisement is from the Chicago Medical Recorder, Volume 37, 1915. Normally $5, but on sale for $2! Wow.

Size: 12" long, 3.5" diameter, 1" thick

X-ray image courtesy of David Allard.

Reference

Grigg, E.R.N. The Trail of the Invisible Light. Charles C Thomas 1965. pages 51 and 634.