iations 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.

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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 soft