n of this machine. Can we find a mechanical or
chemical explanation of the origin of protoplasm? A chemical explanation
of the cell is impossible, since it is not a chemical compound, but a
piece of mechanism. The explanation given for the origin of animals and
plants is also here apparently impossible. The factors upon which that
explanation depended are factors of this completed machine itself, and
can not be used to explain its origin. We are left at present therefore
without any foundation for further advance. The cells must have had a
history of construction, but we do not as yet conceive any forces which
may be looked upon as contributing to that history. Whether life
phenomena can be manifested by any mixture of compounds simpler than the
cell we do not yet know.

The great problems still remaining for solution, which have hardly been
touched by modern biology in all its endeavours to find a mechanical
explanation of the living machine, are, therefore, three. First, the
relation of mentality to the general phenomena of the correlation of
force; second, the intelligible understanding of the mechanism of
protoplasm which enables it to guide the blind chemical and physical
forces of nature so as to produce definite results; third, the kind of
forces which may have contributed to the origin of that simplest living
machine upon whose activities all vital phenomena rest--the living cell.

INDEX.

A.

Absorption of food, 20.

Acquired characters, inheritance of, 164, 165, 166, 167, 171.
--variations, 159, 160.

Amoeba, 73.

Anatomical evidence for evolution, 142.

Aquacity, 80.

Arm compared with wing, 144.

Aristotle, 1.

Assimilation, 80, 124, 149, 176.

Asters of dividing cells, 98.

B.

Barry, 63, 64.

Bathybias, 84.

Biology a new science, 1, 5, 15.

Blood, 35, 36, 38, 69, 73.

Blood-vessels, 35, 36.

Body as a machine, 22, 25, 49.

Bone cells, 69.

Building of the living machine, 131, 134, 136, 137, 167, 175, 180.

C.

Cartilage cells, 68.
Cell as a machine, 126, 128.
--description of, 69.
--division, 95, 96, 101.
--discovery of, 58.
--doctrine, 60.
--substance, 65, 125.

Cells, 56, 84, 86, 118, 119.

Cellular structure of organisms, 65.

Cell wall, 64, 72.

Centrosome, 94, 96, 97, 101, 103, 105, 110.

Challenger expedition, 83.

Chemical evolution, 179.

Chemical theory of vitality, 14;
of life, 78, 116.

Chemism or mechanism, 57, 176.

Chemistry o