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.