or less extent, depart from it. No two individuals have been found in
whom all the Bertillon measurements agree. Disease has reference to
the individual; conditions which in one individual would be regarded
as disease need not be so regarded in another. Comparisons between
health and disease, the normal and the abnormal, must be made not
between the ideal normal and abnormal, but between what constitutes
the normal or usual and the abnormal in a particular individual.

The conception of disease is so inseparably associated with that of
life that a brief review of the structure and properties of living
things is necessary for the comprehension of the definition which has
been given. Living matter is subject to the laws which govern matter,
and like matter of any other sort it is composed of atoms and
molecules. There is no force inherent in living matter, no vital force
independent of and differing from the cosmic forces; the energy which
living matter gives off is counterbalanced by the energy which it
receives. It undergoes constant change, and there is constant
interchange with the environment. The molecules which compose it are
constantly undergoing change in their number, kind and arrangement.
Atom groups as decomposition products are constantly given off from
it, and in return it receives from without other atom groups with
which it regenerates its substance or increases in amount. All
definitions of life convey this idea of activity. Herbert Spencer
says, "Life is the continuous adjustment of internal relations to
external conditions." The molecules of the substances forming the
living material are large, complex and unstable, and as such they
constantly tend to pass from the complex to the simple, from unstable
to stable equilibrium. The elementary substances which form living
material are known, but it has hitherto not been found possible
artificially so to combine these substances that the resulting mass