For example, I once found a tune "in my head" which was perfectly familiar, but for which I could find no words.

Tested on the piano, the pitch was F-sharp and the time was my heart beat.

Finally, after much effort, I got the unworthy words "Wait till the clouds roll by" by humming the tune over repeatedly.

The pitch is determined probably by the accidental condition of the auditory centre in the brain or by the pitch of the external sound which serves as stimulus to the tune.
_Normal Auto-Suggestion._--A further class of Suggestions, which fall under the general phrase Auto-suggestion, or Self-suggestion of a normal type, may be illustrated.

In experimenting upon the possibility of suggesting sleep to another I have found certain strong reactive influences upon my own mental condition.