through the revival of
memories and sentiments and through the persistence of tradition and
culture. Contacts of mobility, on the other hand, define the area of the
interaction of the members of the group in space. The degree of
departure from accepted ideas and modes of behavior and the extent of
sympathetic approach to the strange and the novel largely depend upon
the rate, the number, and the intensity of the contacts of mobility.

b) _Communication as the medium of social interaction._--Each science
postulates its own medium of interaction. Astronomy and physics assume
a hypothetical substance, the ether. Physics has its principles of molar
action and reaction; chemistry studies molecular interaction. Biology
and medicine direct their research to the physiological interaction of
organisms. Psychology is concerned with the behavior of the individual
organism in terms of the interaction of stimuli and responses.
Sociology, as collective psychology, deals with communication.
Sociologists have referred to this process as intermental stimulation
and response.

The readings on communication are so arranged as to make clear the three
natural levels of interaction: (x) that of the senses; (y) that of
the emotions; and (z) that of sentiments and ideas.

Interaction through sense-perceptions and emotional responses may be
termed the natural forms of communication since they are common to man
and to animals. Simmel's interpretation of interaction through the
senses is suggestive of the subtle, unconscious, yet profound, way in
which personal attitudes are formed. Not alone vision, but hearing,
smell and touch exhibit in varying degrees the emotional responses of
the type of appreciation. This means understanding other persons or
objects on the perceptual basis.

The selections from Darwin and from Morgan upon emotional expression in
animals indicate how natural expressive signs become a vehicle for
communication. A prepossession for speech and ideas blinds man to the
important role in human conduct still exerted by emotional
communication, facial expression, and gesture. Blushing and laughter are
peculiarly significant, because these forms of emotional response are
distinctively human. To say that a person blushes when he is
self-conscious, that he laughs when he is detached from, and superior
to, and yet interested in, an occurrence means that blushing and
laughter represent contrasted attitudes to a social situation. The