inside suffused with its Peculiar, yellowish-green light, divided into
two hemispheres of different shades. That, I knew, was the cathode
ray, not the X-ray, for the X-ray itself, which streams outside the
tube, is invisible to the human eye. 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