for the halo would, probably, have been for ever beyond our
cognisance.

THE USE OF RADIUM IN MEDICINE [1]

IT has been unfortunate for the progress of the radioactive
treatment of disease that its methods and claims involve much of
the marvellous. Up till recently, indeed, a large part of
radioactive therapeutics could only be described as bordering on
the occult. It is not surprising that when, in addition to its
occult and marvellous characters, claims were made on its behalf
which in many cases could not be supported, many medical men came
to regard it with a certain amount of suspicion.

Today, I believe, we are in a better position. I think it is
possible to ascribe a rational scientific basis to its legitimate
claims, and to show, in fact, that in radioactive treatment we
are pursuing methods which have been already tried extensively
and found to be of definite value; and that new methods differ
from the old mainly in their power and availability, and little,
or not at all, in kind.

Let us briefly review the basis of the science. Radium is a
metallic element chemically resembling barium. It

[1] A Lecture to Postgraduate Students of Medicine in connection
with the founding of the Dublin Radium Institute, delivered in
the School of Physic in Ireland, Trinity College, on October 2nd,
1914

244

possesses, however, a remarkable property which barium does not.
Its atoms are not equally stable. In a given quantity of radium a
certain very small percentage of the total number of atoms
present break up per second. By "breaking up" we mean their
transmutation to another element. Radium, which is a solid
element under ordinary conditions, gives rise by transmutation to
a gaseous element--the emanation of radium. The new element is a
heavy gas at ordinary temperatures and, like other gases, can be
liquified by extreme cold. The extraordinary property of
transmutation is entirely automatic. No influence which chemist
or physicist can apply can affect the rate of transformation.

The emanation inherits the property of instability, but in its
case the instability is more pronounced. A relatively large
fraction of its atoms transmute per second to a solid element
designated Radium A. In turn this new generation of atoms breaks
up--even faster than the emanation--becoming yet another element
with specific chemical properties. And so on for a whole sequence
of transmutations, till finally a stable substance is fo