This difference, involving a great difference in the possible practical consequences of the two conditions of natural and hypnotic sleep, clearly serves to bring the latter condition nearer to that of insanity than the former condition is brought.

A strong susceptibility to the hypnotic influence, such as Dr.Heidenhain describes, might, indeed, easily prove a very serious want of "adaptation of internal to external relations," whereas a tendency to dreaming would hardly prove a maladaptation at all..