The doctor placed in our hands a couple of fluoroscopes, an
apparatus by which X-rays can be detected. It consists simply of
a closed box with an opening to which the eyes are placed. The
opposite end of the box is a piece of board coated with a salt
such as platino-barium cyanide. When the X-ray strikes this salt
it makes it glow, or fluoresce, and objects held between the
X-ray tube and the fluoroscope cast shadows according to the
density of the parts which the X-rays penetrate.

With the lead-glass bowl removed, the X-ray tube sent forth its
wonderful invisible radiation and made the back of the
fluoroscope glow with light. I could see the bones of my fingers
as I held them up between the X-ray tube and the fluoroscope. But
with the lead-glass bowl in position over the tube, the
fluoroscope was simply a black box into which I looked and saw
nothing. So very little of the radiation escaped from the bowl
that it was negligible--except at one point where there was an
opening in the bottom of the bowl to allow the rays to pass
freely through exactly on the spot on the patient where they were
to be used.

"The dermatitis, they say, has appeared all over her body,
particularly on her head and shoulders," added Dr. Gregory. "Now
I have shown you my apparatus to impress on you how really
impossible it would have been for her to contract it from her
treatments here. I've made thousands of exposures with never an
X-ray burn before--except to myself. As for myself, I'm as
careful as I can be, but you can see I am under the rays very
often, while the patient is only under them once in a while."