rogen. 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.

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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 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 b