s bodies shall we continue to call protoplasm? Shall it be the
linin, or the liquids, or the microsomes, or the chromatin threads, or
the centrosomes? Which of these is the actual physical basis of life?
From the description of cell life which we have given, it will be
evident that no one of them is a material upon which our chemical
biologists can longer found a chemical theory of life. That chemical
theory of life, as we have seen, was founded upon the conception that
the primitive life substance is a definite chemical compound. No such
compound has been discovered, and these disclosures of the microscope of
the last few years have been such as to lead us to abandon hope of ever
discovering such a compound. It is apparently impossible to reduce life
to any simpler basis than this combination of bodies which make up what
was formerly called protoplasm. The term protoplasm is still in use with
different meanings as used by different writers. Sometimes it is used to
refer to the entire contents of the cell; sometimes to the cell
substance only outside the nucleus. Plainly, it is not the protoplasm of
earlier years.

With this conclusion one of our fundamental questions has been answered.
We found in our first chapter that the general activities of animals and
plants are easily reduced to the action of a machine, provided we had
the fundamental vital powers residing in the parts of that machine. We
then asked whether these fundamental properties were themselves those
of a chemical compound or whether they were to be reduced to the action
of still smaller machines. The first answer which biologists gave to
this question was that assimilation, growth, and reproduction were the
simple properties of a complex chemical compound. This answer was
certainly incorrect. Life activities are exhibited by no chemical
compound, but, so far as we know, only by the machine called the cell.
Thus it is that we are again reduced to the problem of understanding the
action of a machine. It may be well to pause here a moment to notice
that this position very greatly increases the difficulties in the way of
a solution of the life problem. If the physical basis of life had proved
to be a chemical compound, the problem of its origin would have been a
chemical one. Chemical forces exist in nature, and these forces are
sufficient to explain the formation of any kind of chemical compound.
The problem of the origin of the life substance would then hav