cts as the chemical
homogeneity of these two kinds of matter, and the conformity of
physiological processes to more general physical laws. Organic matter
differs from inorganic only through the presence of proteid, a peculiar
product of known elements, which cannot be artificially produced, but
which is by natural means perpetually dissolved into these elements
without any discoverable residuum. Respiration may be studied as a case
of aerodynamics, the circulation of the blood as a case of
hydrodynamics, and the heat given off in the course of work done by the
body as a case of thermodynamics. And although vitalistic theories still
retain a place in physiology, as do teleological theories in biology, on
the whole the naturalistic programme of a reduction of organic processes
to the type of the inorganic tends to prevail.

[Sidenote: Mind. The Reduction to Sensation.]

Sect. 114. The history of naturalism shows that, as in the case of life,
so also in the case of _mind_, its hypotheses were projected by the
Greeks, but precisely formulated and verified only in the modern period
of science. In the philosophy of Democritus the soul was itself an atom,
finer, rounder, and smoother than the ordinary, but thoroughly a part of
the mechanism of nature. The processes of the soul are construed as
interactions between the soul and surrounding objects. In sensation, the
thing perceived produces images by means of effluxes which impinge upon
the soul-atom. These images are not true reports of the outer world, but
must be revised by thought before its real atomic structure emerges.
For this higher critical exercise of thought Democritus devised no
special atomic genesis. The result may be expressed either as the
invalidity of such operations of mind as he could provide for in his
universe, or the irreducibility to his chosen first principles of the
very thought which defined them. Later naturalism has generally
sacrificed epistemology to cosmology, and reduced thought to sensation.
Similarly, will has been regarded as a highly developed case of
instinct. Knowledge and will, construed as sensation and instinct, may
thus be interpreted in the naturalistic manner within the field of
biology.

[Sidenote: Automatism.]

Sect. 115. But the actual content of sensation, and the actual feelings
which attend upon the promptings of instinct, still stubbornly testify
to the presence in the universe of something belonging to a wholly
differen