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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-rays or x-rays fall on matter they give rise to ß-rays.
The mechanism involved is not known but it is possibly a result
of the resonance of the atom, or of parts of it, to the short
light waves. And it is remarkable that the y-rays which, as we
have seen, are shorter and more penetrating waves than the
x-rays, give rise to ß-rays possessed of greater velocity and
penetration than ß-rays excited by the x-rays. Indeed the ß-rays
originated by y-rays may attain a velocity nearly approaching
that of light and as great as that of any ß-rays emitted by
transmuting atoms. Again there is demonstrable evidence that
ß-rays impinging on matter may give rise to y-rays. The most
remarkable demonstration of this is seen in the x-ray tube. Here
the x-rays originate where the stream of ß- or cathode-rays
247
are arrested on the anode. But the first relation is at present
of most importance to us--_i.e._ that the y-or x-rays give rise to
ß-rays.
This relation gives us additional evidence of the identity of the
physical effects of y-, x-, and light-rays --using the term light
rays in the usual sense of spectral rays. For it has long been
known that light waves liberate electrons from atoms. It has been
found that these electrons possess a certain initial velocity
which is the greater the shorter the wave length of the light
concerned in their liberation. The whole science of
"photo-electricity" centres round this phenomenon. The action of
light on the photographic plate, as well as many other physical
and chemical phenomena, find an explanation in this liberation of
the electron by the light wave.
Here, then, we have spectral light waves liberating
electrons--_i.e._ very minute negatively-charged particles, and we
find that, as we use shorter light waves, the initial velocity of
these particles increases. Again, we have x-rays which are far
smaller in wave length than spectral light, liberating much
faster negatively electrified particles. Finally, we have
y-rays--the shortest nether waves of all-liberating negative
particles of the highest velocity known. Plainly the whole series
of phenomena is continuous.
We can now look closer at the actions involved in the therapeutic
influence of the several rays and in
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this way, also, see further the correlation between what may be
called photo-therapeutics and radioactive therapeutics.
The ß-ray, whether we obtain it directly from the transforming
radioactive atom or whether we obtain it as a result of the
effects of the y- or x-rays upon the atom, is an ionising agent
of wonderful power. What is meant by this? In its physical aspect
this means that the atoms through which it passes acquire free
electric charges; some becoming positive, some negative. This can
only be due to the loss of an electron by the affected atom. The
loss of the small negative charge carried in the electron leaves
the atom positively electrified or creates a positive ion. The
fixing of the wandering electron to a neutral atom creates a
negative ion. Before further consideration of the importance of
the phenomenon of ionisation we must fix in our minds that the
agent, which brings this about, is the ß-ray. There is little
evidence that the y-ray can directly create ions to any large
extent. But the action of liberating high-speed ß-rays results in
the creation of many thousands of ions by each ß-ray liberated.
As an agent in the hands of the medical man we must regard the
y-ray as a light wave of extremely penetrating character, which
creates high-speed ß-rays in the tissues which it penetrates,
these ß-rays being most potent ionising agents. The ß-rays
directly obtained from radioactive atoms assist in the work of
ionisation. ß-rays do not
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penetrate far from their source. The fastest of them would not
probably penetrate one centimetre in soft tissues.
We must now return to the phenomenon of ionisation. Ionisation is
revealed to observation most conspicuously when it takes place in
a gas. The + and - electric charges on the gas particles endow it
with the properties of a conductor of electricity, the + ions
moving freely in one direction and the - ions in the opposite
direction under an electric potential. But there are effects
brought about by ionisation of more importance to the medical man
than this. The chemist has long come to recognise that in the ion
he is concerned with the inner mechanism of a large number of
chemical phenomena. For with the electrification of the atom
attractive and repulsive forces arise. We can directly show the
chemical effects of the ionising ß-rays. Water exposed to their
bombardment splits up into hydrogen and oxygen. And, again, the
separated atoms may be in part recombined under the influence of
the radiation. Ammonia splits up into hydrogen and nitrogen.
Carbon dioxide forms carbon, carbon monoxide, and oxygen;
hydrochloric acid forms chlorine and hydrogen. In these cases,
also, recombination can be partially effected by the rays.
We can be quite sure that within the complex structure of the
living cell the ionising effects which everywhere accompany the
ß-rays must exert a profound influence. The sequence of chemical
events which as yet seem
250
beyond the ken of science and which are involved in metabolism
cannot fail to be affected. Any, it is not surprising that as the
result of eaperinient it is found that the radiations are agents
which may be used either for the stimulation of the natural
events of growth or used for the actual destruction of the cell.
It is easy to see that the feeble radiation should produce the
one effect, the strong the other. In a similar way by a moderate
light stimulus we create the latent image in the photographic
plate; by an intense light we again destroy this image. The inner
mechanism in this last case can be logically stated.[1]
_There is plainly a true physical basis here for the efficacy of
radioactive treatment and, what is more, we find when we examine
it, that it is in kind not different from that underlying
treatment by spectral radiations. But in degree it is very
different and here is the reason for the special importance of
radioactivity as a therapeutic agent._ The Finsen light is capable
of influencing the soft tissues to a short depth only. The reason
is that the wave length of the light used is too great to pass
without rapid absorption through the tissues; and, further, the
electrons it gives rise to--_i.e._ the ß-rays it liberates--are too
slow-moving to be very efficient ionisers. X-rays penetrate in
some cases quite freely and give rise to much faster and more
powerful ß-rays
[1] See _The Latent Image_, p. 202.
251
than can the Finsen light. But far more penetrating than x-rays
are the y-rays emitted in certain of the radioactive changes.
These give rise to ß-rays having a velocity approximate to that
of light.
The y-rays are, therefore, very penetrating and powerfully
ionising light waves; light waves which are quite invisible to
the eye and can beam right through the tissues of the body. To
the mind's eye only are they visible. And a very wonderful
picture they make. We see the transmuting atom flashing out this
light for an inconceivably short instant as it throws off the
ß-ray. And "so far this little candle throws his beams" in the
complex system of the cells, so far atoms shaken by the rays send
out ß-rays; these in turn are hurled against other atomic
systems; fresh separations of electrons arise and new attractions
and repulsions spring up and the most important chemical changes
are brought about. Our mental picture can claim to be no more
than diagrammatic of the reality. Still we are here dealing with
recognised physical and chemical phenomena, and their description
as "occult" in the derogatory sense is certainly not
justifiable.
Having now briefly reviewed the nature of the rays arising in
radioactive substances and the rationale of their influence, we
must turn to more especially practical considerations.
The Table given opposite shows that radium itself is responsible
for a- and ß-rays only. It happens that
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Period in whioh ½ element is transformed.
URANIUM 1 & 2 { a 6 } x 109 years.
URANIUM X { a ß } 24.6 days.
IONIUM { a 8 } x 104 years.
RADIUM { a ß } 2 x 102 years.
EMANATION { a } 8.85 days.
RADIUM A { a 8 } minutes.
RADIUM B { ß y } 26.7 minutes.
RADIUM C { a ß y } 13.5 minutes.
RADIUM D { ß } 15 years.
RADIUM E { ß y } 4.8 days.
RADIUM (Polonium) F { a } 140 days.
Table showing the successive generations of the elements of the
Uranium-radium family, the character of their radiations and
their longevity.
253
the ß-rays emitted by radium are very "soft"--_i.e._ slow and
easily absorbed. The a-ray is in no case available for more than
mere surface application. Hence we see that, contrary to what is
generally believed, radium itself is of little direct therapeutic
value. Nor is the next body in succession--the emanation, for it
gives only a-rays. In fact, to be brief, it is not till we come
to Radium B that ß-rays of a relatively high penetrative quality
are reached; and it is not till we come to Radium C that highly
penetrative y-rays are obtained.
It is around this element, Radium C, that the chief medical
importance of radioactive treatment by this family of radioactive
bodies centres. Not only are ß-rays of Radium C very penetrating,
but the y-rays are perhaps the most energetic rays of the, kind
known. Further in the list there is no very special medical
interest.
Now, how can we get a supply of this valuable element Radium C?
We can obtain it from radium itself. For even if radium has been
deprived of its emanation (which is easily done by heating it or
bringing it into solution) in a few weeks we get back the Radium
C. One thing here we must be clear about. With a given quantity
of Radium only a certain definitely limited amount of Radium C,
or of emanation, or any other of the derived bodies, will be
associated. Why is this? The answer is because the several
successive elements are themselves decaying --_i.e._ changing one
into the other. The atomic per-
254
centage of each, which decays in a second, is a fixed quantity
which we cannot alter. Now if we picture radium which has been
completely deprived of its emanation, again accumulating by
automatic transmutation a fresh store of this element, we have to
remember:-- (i) That the rate of creation of emanation by the
radium is practically constant; and (2) that the absolute amount
of the emanation decaying per second increases as the stock of
emanation increases. Finally, when the amount of accumulated
emanation has increased to such an extent that the number of
emanation atoms transmuting per second becomes exactly equal to
the number being generated per second, the amount of emanation
present cannot increase. This is called the equilibrium amount.
If fifteen members are elected steadily each year into a
newly-founded society the number of members will increase for the
first few years; finally, when the losses by death of the members
equal about fifteen per annum the society can get no bigger. It
has attained the equilibrium number of members.
This applies to every one of the successive elements. It takes
twenty-one days for the equilibrium quantity of emanation to be
formed in radium which has been completely de-emanated; and it
takes 3.8 days for half the equilibrium amount to be formed.
Again, if we start with a stock of emanation it takes just three
hours for the equilibrium amount of Radium C to be formed.
255
We can evidently grow Radium C either from radium itself or from
the emanation of radium. If we use a tube of radium we have an
almost perfectly constant quantity of Radium C present, for as
fast as the Radium C and intervening elements decay the Radium,
which only diminishes very slowly in amount, makes up the loss.
But, if we start off with a tube of emanation, we do not possess
a constant supply of Radium C, because the emanation is decaying
fairly rapidly and there is no radium to make good its loss. In
3.8 days about one half the emanation is transmuted and the
Radium C decreases proportionately and, of course, with the
Radium C the valuable radiations also decrease. In another 3.8
days--that is in about a week from the start--the radioactive value
of the tube has fallen to one-fourth of its original value.
But in spite of the inconstant character of the emanation tube
there are many reasons for preferring its use to the use of the
radium tube. Chief of these is the fact that we can keep the
precious radium safely locked up in the laboratory and not
exposed to the thousand-and-one risks of the hospital. Then,
secondly, the emanation, being a gas, is very convenient for
subdivision into a large number of very small tubes according to
the dosage required.
In fact the volume of the emanation is exceedingly minute. The
amount of emanation in equilibrium with one gramme of radium is
called the curie, and with one
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milligramme the millicurie. Now, the volume of the curie is only
a little more than one half a cubic millimetre. Hence in dealing
with emanation from twenty or forty milligrammes of radium we are
dealing with very small volumes.
How may the emanation be obtained? The process is an easy one in
skilled and practised hands. The salt of radium--generally the
bromide or chloride--is brought into acid solution. This causes
the emanation to be freely given off as fast as it is formed. At
intervals we pump it off with a mercury pump.
Let us see how many millicuries we will in future be able to turn
out in the week in our new Dublin Radium Institute.[1] We shall
have about 130 milligrammes of radium. In 3.8 days we get 65
millicuries from this--_i.e._ half the equilibrium amount of 130
millicuries. Hence in the week, we shall have about 130
millicuries.
This is not much. Many experts consider this little enough for
one tube. But here in Dublin we have been using the emanation in
a more economical and effective manner than is the usage
elsewhere; according to a method which has been worked out and
developed in our own Radium Institute. The economy is obtained by
the very simple expedient of minutely subdividing the' dose. The
system in vogue, generally, is to treat the tumour by inserting
into it one or two very active
[1] Then recently established by the Royal Dublin Society.
257
tubes, containing, perhaps, up to 200 millicuries, or even more,
per tube. Now these very heavily charged tubes give a radiation
so intense at points close to the tube, due to the greater
density of the rays near the tube, and, also, to the action of
the softer and more easily absorbable rays, that it has been
found necessary to stop these softer rays--both the y and ß--by
wrapping lead or platinum round the tube. In this lead or
platinum some thirty per cent. or more of the rays is absorbed
and, of course, wasted. But in the absence of the screen there is
extensive necrosis of the tissues near the tubes.
If, however, in place of one or two such tubes we use ten or
twenty, each containing one-tenth or one-twentieth of the dose,
we can avail ourselves of the softer rays around each tube with
benefit. Thus a wasteful loss is avoided. Moreover a more uniform
"illumination" of the tissues results, just as we can illuminate
a hall more uniformly by the use of many lesser centres of light
than by the use of one intense centre of radiation. Also we get
what is called "cross-radiation,"which is found to be beneficial.
The surgeon knows far better what he is doing by this method.
Thus it may be arranged for the effects to go on with approximate
uniformity throughout the tumour instead of varying rapidly
around a central point or--and this may be very important-- the
effects may be readily concentrated locally.
Finally, not the least of the benefit arises in the easy
technique of this new method. The quantities of
258
emanation employed can fit in the finest capillary glass tubing
and the hairlike tubes can in turn be placed in fine exploring
needles. There is comparatively little inconvenience to the
patient in inserting these needles, and there is the most perfect
control of the dosage in the number and strength of these tubes
and the duration of exposure.[1]
The first Radium Institute in Ireland has already done good work
for the relief of human suffering. It will have, I hope, a great
future before it, for I venture, with diffidence, to hold the
opinion, that with increased study the applications and claims of
radioactive treatment will increase.
[1] For particulars of the new technique and of some of the work
already accomplished, see papers, by Dr. Walter C. Stevenson,
_British Medical Journal_, July 4th, 1914, and March 20th, 1915.
259