Pay particular attention to these definitions, as "groups" of ideas and
"complexes" of ideas, emotions and muscular movements are terms that we
shall constantly employ.

You learned in a former lesson that mental experiences may consist not
only of sense-perceptions based on excitements arising in the memory
nerves, but also of bodily emotions, the "feeling tones" of ideas, and
of muscular movements based on stimuli arising in the motor nerves.

_Groups consist, therefore, not only of associated ideas, but of
associated ideas coupled with their emotional qualities and impulses to
muscular movements._

All groups bound together by a mutually related idea constitute a single
"complex." Every memory you have is an illustration of such "complexes."

[Sidenote: _The Thrill of Recollection_]

Suppose, for example, you once gained success in a business deal. Your
recollection of the other persons concerned in that transaction, of any
one detail in the transaction itself, will be accompanied by the faster
heartbeat, the quickened circulation of the blood, the feeling of
triumph and elation that attended the original experience.

[Sidenote: _"Complexes" and Functional Derangements_]

Complexes formed out of harrowing earthquakes, robberies, murders or
other dreadful spectacles, which were originally accompanied on the part
of the onlooker by trembling, perspiration and palpitation of the