, even to many minute details--such, for instance, as
the inheritance of a congenital mark--it becomes evident that the egg is
a body of extraordinary complexity. And yet the egg is nothing more than
a single cell agreeing with other cells in all its general characters.
It is clear, then, that we must look upon organization as something
superior to cells and something existing within them, or at least within
the egg cell, and controlling its development. We are forced to believe,
further, that there may be as important differences between two cells as
there are between two adult animals or plants. In some way there must be
concealed within the two cells which constitute the egg of the starfish
and the man differences which correspond to the differences between the
starfish and the man. Organization, in other words, is superior to cell
structure, and the cell itself is an organization of smaller units.

As the result of these various considerations there has been, in recent
years, something of a reaction against the cell doctrine as formerly
held. While the study of cells is still regarded as the key to the
interpretation of life phenomena, biologists are seeing more and more
clearly that they must look deeper than simple cell structure for their
explanation of the life processes. While the study of cells has thrown
an immense amount of light upon life, we seem hardly nearer the centre
of the problem than we were before the beginning of the series of
discoveries inaugurated by the formulation of the doctrine of
protoplasm.

==Fundamental Vital Activities as Located in Cells.==--We are now in
position to ask whether our knowledge of cells has aided us in finding
an explanation of the fundamental vital actions to which, as we have
seen, life processes are to be reduced. The four properties of
irritability, contractibility, assimilation, and reproduction, belong to
these vital units--the cells, and it is these properties which we are
trying to trace to their source as a foundation of vital activity.

We may first ask whether we have any facts which indicate that any
special parts of the cell are associated with any of these fundamental
activities. The first fact that stands out clearly is that the nucleus
is connected most intimately with the process of reproduction and
especially with heredity. This has long been believed, but has now been
clearly demonstrated by the experiments of cutting into fragments the
cell bodies