, when any sort of an image forces itself into the
consciousness as something complete, whether it is in the form of an
idea that suddenly emerges and dominates consciousness, or a vision, a
premonition, or the like.

In all these cases psychic influences which have arisen without external
stimulus have directly inoculated the mind, thereby evading the
criticism of the "ego" or of personal consciousness.

"Suggesting" signifies, therefore, to inoculate the mind of a person
more or less directly with ideas, feelings, emotions, and other
psychical states, in order that no opportunity is left for criticism and
consideration. Under "suggestion," on the other hand, is to be
understood that sort of direct inoculation of the mind of an individual
with ideas, feelings, emotions, and other psychophysical states which
evade his "ego," his personal self-consciousness, and his critical
attitude.

Now and then, especially in the French writers, one will find besides
"suggestion" the term "psychic contagion," under which, however, nothing
further than involuntary imitation is to be understood (compare A.
Vigouroux and P. Juquelier, _La contagion mentale_, Paris, 1905). If one
takes up the conception of suggestion in a wider sense, and considers
by it the possibility of involuntary suggestion in the way of example
and imitation, one will find that the conceptions of suggestion and of
psychic contagion depend upon each other most intimately, and to a great
extent are not definitely to be distinguished from each other. In any
case, it is to be maintained that a strict boundary between psychic
contagion and suggestion does not always exist, a fact which Vigouroux
and Juquelier in their paper have rightly emphasized.

2. The Subtler Forms of Suggestion[152]

In one very particular respect hypnotism has given us a lesson of the
greatest importance to psychology: it has proved that special
precautionary measures must be taken in planning psychological
experiments. The training of hypnotics has thrown light on this source
of error. A hypnotizer may, often without knowing it, by the tone of his
voice or by some slight movement cause the hypnotic to exhibit phenomena
that at first could only be produced by explicit verbal suggestion, and
that altogether the signs used by the hypnotizer to cause suggestions
may go on increasing in delicacy. A dangerous source of error is
provided by the hypnotic's endeavor to divine and obey the
experim