93. The voluntary or involuntary intervention of a person endowed with a
special aptitude for the production of these phenomena appears to be necessary in the
greater number of cases, although cases occur in which the spirit appears to act alone;
but even then, it is quite possible that he may draw the animalised fluid from some
other source than the persons present : a possibility which explains why It IS that
spirits, though incessantly around us, do not always exert a perturbing action. To do
this, it is necessary, first, that the spirit should will it, and, secondly, that he should have
some motive for doing it; otherwise, he does nothing. It is also necessary for him to
find, precisely in the place where he wishes to act, the person or persons fitted to
second his action; a coincidence of comparatively rare occurrence. If an available
person enters unexpectedly, the spirit may profit by the opportunity thus afforded; or, in
spite of the concurrence of favourable circumstances, he may be prevented from acting
by some superior will, which does not permit him to act as he wishes. He may be only
permitted to act under certain limitations, and in a case in which the manifestations he
wishes to produce would be useful, either as a means of conviction, or as a test for the
person who is the object of them.
