constituent cells. Should these units be subtracted from an animal, one by
one, there would be no material organism left when the last cells had been
disassociated, and there would be no organic activity remaining when the
last individual cell-life was destroyed. All the various things we do in
the performance of our daily tasks are done by the combined action of our
muscle and nerve and other tissue cells; our life is all of their lives,
and nothing more. The cell, then, is the physiological or functional unit,
as truly as it is the material element of the organic world. Being
combined with countless others, specialized in various ways, relations are
established which are like those exhibited by the human beings
constituting a nation. In this case the life of the community consists of
the activities of the diverse human units that make it up. The farmer, the
manufacturer, the soldier, clerk, and artisan do not all work in the same
way; they undertake one or another of the economic tasks which they may be
best fitted by circumstances to perform. Their differentiation and
division of labor are identical with the diversity in structure and in
function as well, exhibited by the cells of a living creature. We might
speak of the several states as so many organs of our own nation; the
commercial or farming or manufacturing communities of a state would be
like the tissues forming an organ, made up ultimately of human units,
which, like cells, are engaged in similar activities. As the individual
human lives and the activities of differentiated economic groups
constitute the life of a nation and national existence, so cell-lives make
the living of an organism, and the expressions "division of labor" and
"differentiation" come to have a biological meaning and application.

* * * * *

The cell, then, is in all respects the very unit of the organic world. Not
only is it the ultimate structural element of all the more familiar