whole
process going at the proper rate, and with the different parts of the whole
factory working in smooth coordination with each other. Any disturbance of
the mechanism in any particular room, or any abnormal condition which
breaks down the coordination or results in the mixing of the reagents or
processes of adjoining rooms in improper order or proportions, produces
instant destruction of the normal process, abnormal reactions take place,
and the factory output is interrupted.

No other conception than this one of a definite structure and coordination
of the different working parts of a cell can adequately account for the
great variety of chemical changes which are constantly going on in any
given cell. It is wholly inconceivable that a homogeneous mass of all the
varying chemical compounds which are contained in any given quantity of
protoplasm could either exist or produce any regular sequence of chemical
reactions. Structure, or organization of the cell-contents into separate
colloidal compartments, and the segregation of cell-contents into masses
having different functions, is essential to any reasonable conception of
how the cell performs its various activities.

The best understanding of the structural arrangement is afforded by the
conception that protoplasm consists of a colloidal gel, or sometimes a very
viscid sol, containing water, salts, carbohydrates, fats, proteins, and
enzymes. Evidence in favor of this conception is afforded by the appearance
of protoplasm under a high-power microscope, and by the close resemblance
of the processes which go on in it, and its responses to external stimuli,
to those of an artificial gel of similar chemical composition.

Two different conceptions of the form in which the chemical components
exist in this mass have been advanced. One is that they are in true
molecular unions, known as "biogens," and that the reactions which take
place in the mass may, therefore, be studied from the same basis as are
reactions between similar substances when they take place in a beaker or
test tube in the laboratory. It would seem, however, that the constantly
varying proportions of the materials themselves, and the lack of
homogeneity of cell contents, afford insurmountable difficulties to this
conception as a basis for the study of cell activities. The other, and
seemingly more reasonable, conception is that these bodies exist in the
form of colloidal complexes, whose composition may v