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 trans.m.u.tations

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upon medical science? Radium or emanation, &c., are not in the Pharmacopoeia as are, say, a.r.s.enic or bis.m.u.th. The whole medicinal value of these elements resides in the very wonderful phenomena of their radiations. They radiate in the process of trans.m.u.ting.

The changing atom may radiate a part of its own ma.s.s. 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 const.i.tuent 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.

Trans.m.u.ting atoms give out also material rays of another kind: the -rays. The -ray is in ma.s.s 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 -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.

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Another and quite different kind of radiation is given out by many of the trans.m.u.ting 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 trans.m.u.ting atom along with the -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 -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 -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 -rays possessed of greater velocity and penetration than -rays excited by the x-rays. Indeed the -rays originated by y-rays may attain a velocity nearly approaching that of light and as great as that of any -rays emitted by trans.m.u.ting atoms. Again there is demonstrable evidence that -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 - or cathode-rays

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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 -rays.

This relation gives us additional evidence of the ident.i.ty 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 -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 pa.s.ses 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 -ray. There is little evidence that the y-ray can directly create ions to any large extent. But the action of liberating high-speed -rays results in the creation of many thousands of ions by each -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 -rays in the tissues which it penetrates, these -rays being most potent ionising agents. The -rays directly obtained from radioactive atoms a.s.sist in the work of ionisation. -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 -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 -rays must exert a profound influence. The sequence of chemical events which as yet seem

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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 pa.s.s without rapid absorption through the tissues; and, further, the electrons it gives rise to--_i.e._ the -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 -rays

[1] See _The Latent Image_, p. 202.

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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 -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 trans.m.u.ting atom flashing out this light for an inconceivably short instant as it throws off the -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 -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 -rays only. It happens that

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Period in whioh element is transformed.

URANIUM 1 & 2 { a 6 } x 109 years.

URANIUM X { a } 24.6 days.

IONIUM { a 8 } x 104 years.

RADIUM { a } 2 x 102 years.

EMANATION { a } 8.85 days.

RADIUM A { a 8 } minutes.

RADIUM B { y } 26.7 minutes.

RADIUM C { a y } 13.5 minutes.

RADIUM D { } 15 years.

RADIUM E { 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.

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the -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 -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.