e these changes not to a force, but
to the absence of a force. And this is true. Strictly speaking, the
changes should be attributed to those forces which come into action when
the antagonist force is withdrawn. But though there is an inaccuracy in
saying that the freezing of water is due to the loss of its heat, no
practical error arises from it; nor will a parallel laxity of expression
vitiate our statements respecting the multiplication of effects. Indeed,
the objection serves but to draw attention to the fact, that not only
does the exertion of a force produce more than one change, but the
withdrawal of a force produces more than one change. And this suggests
that perhaps the most correct statement of our general principle would
be its most abstract statement--every change is followed by more than
one other change.

Returning to the thread of our exposition, we have next to trace out, in
organic progress, this same all-pervading principle. And here, where the
evolution of the homogeneous into the heterogeneous was first observed,
the production of many changes by one cause is least easy to
demonstrate. The development of a seed into a plant, or an ovum into an
animal, is so gradual, while the forces which determine it are so
involved, and at the same time so unobtrusive, that it is difficult to
detect the multiplication of effects which is elsewhere so obvious.
Nevertheless, guided by indirect evidence, we may pretty safely reach
the conclusion that here too the law holds.

Observe, first, how numerous are the effects which any marked change
works upon an adult organism--a human being, for instance. An alarming
sound or sigh, besides the impressions on the organs of sense and the
nerves, may produce a start, a scream, a distortion of the face, a
trembling consequent upon a general muscular relaxation, a burst of
perspiration, an excited action of the heart, a rush of blood to the
brain, followed possibly by arrest of the heart's action and by syncope:
and if the system be feeble, an indisposition with its long train of
complicated symptoms may set in. Similarly in cases of disease. A minute
portion of the small-pox virus introduced into the system, will, in a
severe case, cause, during the first stage, rigors, heat of skin,
accelerated pulse, furred tongue, loss of appetite, thirst, epigastric
uneasiness, vomiting, headache, pains in the back and limbs, muscular
weakness, convulsions, delirium, etc.; in the second