38 ECONOMIC PRINCIPLES

products, but so that we may treat the comparative results
as if they were the results of alternative applications of the
same labour-power, aided by the necessary machines, etc.
required to give effect to labour.
The development of the subject in relation to the values
of products as to which an exchange can be fairly readily
effected, between the industries concerned, of the labour and
capital engaged in their production, will be taken up in the
following chapter.
When the readjustment of the productive facilities
between different industries cannot be made, the final
adjustment of exchange values, though by no means independent
 of the conditions of supply, and of the variations
in these conditions which may be induced by changes in
the values, is more immediately dependent on the play of
reciprocal demand. The transference of a part of the
producing forces from the one industry to the other being
blocked, the conditions of supply in each industry are only
affected by the conditions of the other industry through the
greater or less abundance of the products of that other
industry which are available for exchange against its own.
This case has a special application in reference to international
 trade, and it will be taken up again in that
connection. It has no small importance in regard to
domestic industry, however, especially in reference to the
exchange of the products of groups of workers between
which there is no direct or indirect exchange of producing
forces. Thus the hand-workers and the brain-workers are, to
a considerable extent, separate groups in this sense. The
selection of an industry for a youth entering on life depends
on his faculties, and while a choice between different manual
trades may be possible for one, a choice between different
smployments of the soft-handed type for another, the choice
between hard-handed and soft-handed trades is only possible
for the same individual in a limited degree. Thus the
supplies of producing energy in these different groups are
largely independent of one another, and the rates of exchange
 of their products are more obviously and directly
dependent on the conditions of reciprocal demand, than