mal incessantly
transforms into its own substance the molecules of surrounding bodies,
later to reject these molecules when they have become heterogeneous to
it. Through this first class of functions the animal exists only
within itself; through the other class it exists outside; it is an
inhabitant of the world, and not, like the plant, of the place which
saw its birth. The animal feels and perceives its surroundings,
reflects its sensations, moves of its own will under their influence,
and, as a rule, can communicate by its voice its desires and its
fears, its pleasures or its pains. I call organic life the sum of the
functions of the former class, for all organised creatures, plants or
animals, possess them to a more or less marked degree, and organised
structure is the sole condition necessary to their exercise. The
combined functions of the second class form the 'animal' life, so
named because it is the exclusive attribute of the animal kingdom"
(pp. 2-3).

In both lives there is a double movement, in the animal life from the
periphery to the centre and from the centre to the periphery, in the
organic life also from the exterior to the interior and back again,
but here a movement of composition and decomposition. As the brain
mediates between sensation and motion, so the vascular system is the
go-between of the organs of assimilation and the organs of
dissimilation.

The most essential structural difference between the organs of animal
life and the organs of organic life is in man and the higher animals
at least, the symmetry of the one set and the irregularity of the
other--compare the symmetry of the nerves and muscles of the animal
life with the asymmetrical disposition of the visceral muscles and the
sympathetic nerves, which belong to the organic life.

Noteworthy differences exist between the two lives with respect to the
influence of habit. Everything in the animal life is under the
dominion of habit. Habit dulls sensation, habit strengthens the
judgment. In the organic life, on the contrary, habit exercises no
influence. The difference comes out clearly in the development of the
individual. The organs of the organic life attain their full
perfection independently of use; the organs of the animal life require
an education, and without education they do not reach perfection
(_Loc. cit._, p. 127).

Bichat was the founder of what was known for a time as General
Anatomy--the study of the constituent tissue