gular capacity for bringing apparently dissimilar facts into
harmony, by finding out the common underlying principle, and, although
we no longer accept this particular conclusion, we cannot fail to
notice in it the peculiar powers of his mind.

A second and even more interesting Royal Institution lecture dealt
with the "Identity of Structure in Animals and Plants." At the present
time every educated person knows that the life of animals and plants
alike depends on the fact that their bodies are composed of a living
material called protoplasm, a material which is identical in every
important respect in both kingdoms of the living world. In the early
fifties, scientific opinion was by no means clear on this matter, and
certainly public opinion was most vague. Huxley discussed what was
meant by organisation, and shewed that in every essential respect
plants and animals alike were organised beings. Then he went on to
explain the cellular theory of Schwann, which was then a novelty to a
general audience. Schwann, in studying the microscopic structure of
plants, noticed that their bodies were made up of little cases with
firm walls; these he called _cells_, and declared that the whole body
of the plant was composed of cells. As the walls of these cells were
the most obvious and visible feature, it was supposed that they were
the most essential part of the structure, and there was some
difficulty in applying the cellular theory to the bodies of animals,
as in most cases there are no easily visible cell-walls in animal
tissues. As the result of his own observation, and from his reading of
the work of others, Huxley laid down in the clearest way what is now
accepted by everyone--that the presence of walls is of minor
importance, and that it is the slimy contents of the cells, what is
called "protoplasm," that is the important element. He declared that
the protoplasm of animals was identical with the protoplasm of plants,
and that plants were "animals confined in wooden cases." He agreed
with Schwann that the cell, using the term to imply the contents
rather than the wall, was of fundamental importance, and was the unit
of structure of the whole world of life. On the other hand, he
declared that it could not be looked at as the unit of function: he
denied that the powers and properties of a living body were simply the
sum of the powers and properties of the single cells. In this opinion
he was not followed by physiologists until