Abstract
The question of the selective power of tissues,
by which they can abstract from the medium in
which they are placed those substances which are
necessary for their life and function, opens up many
problems of fundamental importance in biology. There
are points of uniformity between all cells. Every
cell respires. Every cell absorbs nutrient material
and excretes the indigestible and the effete. But
each cell is an independent unit which chooses for
itself the substances required for its growth, its
development and its functions; and some cells devote
their energies to the elaboration of material not for
their own individual needs, but for the fulfillment of
a function beyond the narrow limits of their own cell-walls.
It is to.the study of this selective power that
I shall devote my thesis. No tissue of the body
seems to me to possess this prophetic power of selection
in so eminent a degree as the Mammary Gland, engaged
as it is in the elaboration of a material adapted to the
requirements not of its own cells, not
of the organism of which it forms a part, but of an
entirely different organism. I propose to enter,
after describing some of the most striking phenomena
of selective activity as exemplified in other tissues
into the subject of the Chemistry of the Mammary
Gland and its secretion, with special reference to
the production,in different species, of milk suited
for the diverse needs of the sucklings of these
species. The work on the Mammary gland and much of
that on the chemistry of milk has been carried out
by me in the Physiological Laboratory of Edinburgh
University. As for the rest I hope to submit a
digest and a criticism of the work of others, some
of which may not be widely known, and all, I trust,
will be of Physiological interest and practical importance.
