along the surface of the glass by the extension of blunt processes
formed from the clear outer portion which adhere to the surface and
into which the interior granular mass flows. This movement does not
take place by chance, but in definite directions, and may be
influenced. The amoeba will move towards certain substances which may
be placed in the fluid around it and away from others. In the water in
which the amoebæ live there are usually other organisms, particularly
bacteria, on which they feed. When such a bacterium comes in contact
with an amoeba, it is taken into its body by becoming enclosed in
processes which the amoeba sends out. The enclosed organism then lies
in a small clear space in the amoeba, surrounded by fluid which has
been shown to differ in its chemical reaction from the general fluid
of the interior. This clear space, which may form at any point in the
body, corresponds to a stomach in a higher animal and the fluid within
it to the digestive fluid or gastric juice. After a time the enclosed
organism disappears, it has undergone solution and is assimilated;
that is, the substances of which its body was composed have been
broken up, the molecules rearranged, and a part has been converted
into the substance of the amoeba. If minute insoluble substances, such
as particles of carmine, are placed in the water, these may also be
taken up by the amoeba; but they undergo no change, and after a time
they are cast out. Under the microscope only the gross vital
phenomena, motion of the mass, motion within the mass, the reception
and disintegration of food particles, and the discharge of inert
substances can be observed. The varied and active chemical changes
which are taking place cannot be observed.

[Illustration: FIG. 2.--AMOEBA. 1. Nucleus. 2. Contractile vesicle.
3. Nutritive vacuole containing a bacillus.]