opposing empiricists to pay more and more attention to the
dialectical character of the operations of nature. The old stiff
antagonisms, the sharp impassable frontier lines are becoming more and
more abolished. Since the last "true" gases have been liquefied, since
the proof that a body can be put in a condition in which liquid and
gaseous forms cannot be differentiated, aggregate conditions have to
the last remnant lost their earlier absolute character. With the
statement of the kinetic theory of gases that, in gases, the squares
of the speeds with which the separate gas molecules move are in
inverse ratio to the molecular weights, under the same temperature,
heat takes its place directly in the series of such measurable forms
of motion. Ten years ago the newly discovered great fundamental law of
motion was still understood as a mere law of the conservation of
energy, as a mere expression of the indestructibility and
uncreatibility of motion, and therefore merely on its quantitative
side. That narrow negative expression has been more and more
subordinated to the transformation of energy, in which the qualitative
content of the process is duly recognised and the last notion of an
extramundane Creator is destroyed. That the quantity of motion (of
energy, so called) is not changed when it is transformed into kinetic
energy (mechanical force, so called), into electricity, heat,
potential static energy need not now be preached any longer as
something new, it served as the foundation, once attained, of many
valuable investigations of the process of transformation itself, of
the great fundamental process, in the knowledge of which is
comprehended the knowledge of all nature. And since biology has been
treated in the light of the theory of evolution it has abolished one
stiff line of classification after another in the realm of organic
nature. The entirely unclassified intermediate conditions increase in
number every day. Later investigations throw organisms out of one
class into another, and marks of distinction which have become
articles of faith lose their individual reality. We have now mammals
which lay eggs and, if the news is established, birds also which go on
all fours. It was already observed, before the time of Virchow, as a
conclusion of the discovery of the cell, that the identity of the
individual creature is lost, scientifically and dialectically
speaking, in a federation of cells, so the idea of animal (and
th