ntimate vital characteristics, such as the infinitely fine structure of
protoplasm. For protoplasm does not fill the cell as a compact mass, but
spreads itself out and builds itself up in the most delicate network or
meshwork, of which it forms the threads and walls, enclosing innumerable
vacuoles and alveoli, and Buetschli succeeded in making a surprisingly good
imitation of this "structure" by mechanical means. Drops of oil intimately
mixed with potash and placed between glass plates formed a very similar
emulsion-like or foam-like structure with a visible network and with
enclosed alveoli.(62)

Rhumbler, too, succeeded in explaining by "developmental mechanics" some
of the apparently extremely subtle processes at the beginning of embryonic
development (the invagination of the blastula to form the gastrula); by
imitating the sphere of cells which compose the blastula with elastic
steel bands he deduced the invagination mechanically from the model.(63)

Here, too, must be mentioned Verworn's attempts to explain "the movements
of the living substance."(64) "Kinesis," the power to move, has since the
time of Aristotle been regarded as one of the peculiar characteristics of
life. From the gliding "amoeboid" movements of the moneron, with its
mysterious power of shifting its position, spreading itself out, and
spinning out long threads ("pseudopodia"), up to the contractility of the
muscle-fibre, the same riddle reappears in many different forms. Verworn
attacks it at the lowest level, and attempts to solve it by reference to
the surface tension to which all fluid bodies are subject, and to the
partial relaxation of this, which forces the mass to give off radiating
processes or "pseudopodia." The mechanical causes of the suspension of the
surface tension are inquired into, and striking examples of pseudopod-like
rays are found in the inorganic world, for instance, in a drop of oil.
Thus a starting-point is discovered for mechanical interpretations at a
higher level.(65)

Irritability.

3. A property which seems to be quite peculiar to living matter is
irritability, or the power of responding to "stimuli," that is to say, of
reacting to some influence from without in such a manner that _the
reaction_ is not the mere equivalent of the action, but that the stimulus
is to the organism as a contingent cause or impulse setting up a new
process or a new series of processes, which seem as though they occurred
spontaneou