teaches us how, hand in hand therewith, the soul itself, as function of
the brain, has been developed. The last-named science teaches us also
that a primitive form of soul-activity is already present even in the
lowest animals, the single-celled primitive animals, Infusoria and
Rhizopoda. Every scientific man who has long observed the life-activity
of these single-celled Protista, is positively convinced that they also
possess a soul; that this "cell-soul" also consists of a sum of
sensations, perceptions, and volitions; the feeling, thinking, and
willing of our human soul differ from these only in degree. In like
manner there is present in the egg-cell (as potential energy) a
hereditary cell-soul, out of which man, like every other animal, is
developed.[15]

The first task of a truly scientific psychology will therefore be, not,
as hitherto, idle speculation about an independent immaterial
soul-existence and its puzzling temporary connection with the animal
body, but rather the comparative investigation of the organs of the soul
and the experimental examination of their psychical functions. For
scientific psychology is a part of physiology, the doctrine of the
functions and the life-activities of organisms. The psychology and
psychiatry of the future, like the physiology and pathology of to-day,
must take the form of a cellular study, and in the first instance
investigate the soul-functions of the cells. Max Verworn, in his fine
_Psycho-physiological Protistastudies_, has lately shown us what
important disclosures such a cellular psychology can make, even in
dealing with the lowest grades of organic life, in the single-celled
Protista (especially Rhizopoda and Infusoria).

These same main divisions of soul-activity, which are to be met with in
the single-celled organism,--the phenomena of irritability, sensation,