ing organisms alone react in a formative or
deformative way to external stimuli. In warm climates the fur of
animals and the wool of sheep become thin and light. The colder the
climate, the thicker these coverings. Such facts only show that in the
matter of adaptation among living organisms, there is a factor at work
other than chemistry and physics--not independent of them, but making a
purposive use of them. Cut off the central shoot that leads the young
spruce tree upwards, and one of the shoots from the whirl of lateral
branches below it slowly rises up and takes the place of the lost
leader. Here is an action not prompted by the environment, but by the
morphological needs of the tree, and it illustrates how different is its
unity from the unity of a mere machine. I am only aiming to point out
that in all living things the material forces behave in a purposive way
to a degree that cannot be affirmed of them in non-living, and that,
therefore, they imply intelligence.

Evidently the cells in the body do not all have the same degree of
life,--that is, the same degree of irritability. The bone cells and the
hair cells, for instance, can hardly be so much alive--or so
irritable--as the muscle cells; nor these as intensely alive as the
nerve and brain cells. Does not a bird possess a higher degree of life
than a mollusk, or a turtle? Is not a brook trout more alive than a
mud-sucker? You can freeze the latter as stiff as an icicle and
resuscitate it, but not the former. There is a scale of degrees in life
as clearly as there is a scale of degrees in temperature. There is an
endless gradation of sensibilities of the living cells, dependent
probably upon the degree of differentiation of function. Anaesthetics
dull or suspend this irritability. The more highly developed and complex
the nervous system, the higher the degree of life, till we pass from
mere physical life to psychic life. Science might trace this difference
to cell structure, but what brings about the change in the character of
the cell, or starts the cells to building a complex nervous system, is a
question unanswerable to science. The biologist imagines this and that
about the invisible or hypothetical molecular structure; he assigns
different functions to the atoms; some are for endosmosis, others for
contraction, others for conduction of stimuli. Intramolecular oxygen
plays a part. Other names are given to the mystery--the micellar strings
of Naegeli, the b