rmed,
identical with ordinary lead in chemical and physical properties,
but possessing a slightly lower atomic weight.

The genealogy of the radium series of elements shows that radium
is not the starting point. It possesses ancestors which have been
traced back to the element uranium.

Now what bearing has this series of transmutations

245

upon medical science? Radium or emanation, &c., are not in the
Pharmacopoeia as are, say, arsenic or bismuth. The whole
medicinal value of these elements resides in the very wonderful
phenomena of their radiations. They radiate in the process of
transmuting.

The changing atom may radiate a part of its own mass. The
"alpha"-ray (a-ray) is such a material ray. It is an electrified
helium atom cast out of the parent atom with enormous
velocity--such a velocity as would carry it, if not impeded, all
round the earth in two seconds. All alpha-rays are positively
electrified atoms of the element helium, which thereby is shown
to be an integral constituent of many elements. The alpha-ray is
not of much value to medical science, for, in spite of its great
velocity, it is soon stopped by encounter with other atoms. It
can penetrate only a minute fraction of a millimetre into
ordinary soft tissues. We shall not further consider it.

Transmuting atoms give out also material rays of another kind:
the ss-rays. The ss-ray is in mass but a very small fraction of,
even, a hydrogen atom. Its speed may approach that of light. As
cast out by radioactive elements it starts with speeds which vary
with the element, and may be from one-third to nine-tenths the
velocity of light. The ss-ray is negatively electrified. It has
long been known to science as the electron. It is also identical
with the cathode ray of the vacuum tube.

246

Another and quite different kind of radiation is given out by
many of the transmuting elements:--the y-ray. This is not
material, it is ethereal. It is known now with certainty that the
y-ray is in kind identical with light, but of very much shorter
wave length than even the extreme ultraviolet light of the solar
spectrum. The y-ray is flashed from the transmuting atom along
with the ss-ray. It is identical in character with the x-ray but
of even shorter wave length.

There is a very interesting connection between the y-ray and the
ss-ray which it is important for the medical man to understand--as
far as it is practicable on our present knowledge.

When y-ray