And, in states of insanity, we see the process of nervous dissolution beginning with these same nervous structures, and so taking the reverse order of the process of evolution.[67] And thus, we may say that throughout the mental life of the most sane of us, these higher and more delicately balanced structures are constantly in danger of being reduced to that state of inefficiency, which in its full manifestation is mental disease.
Does this way of putting the subject seem alarming?
Is it an appalling thought that our normal mental life is thus intimately related to insanity, and graduates away into it by such fine transitions?
A moment's reflection will show that the case is not so bad as it seems.
It is well to remind ourselves that the brain is a delicately adjusted organ, which very easily gets disturbed, and that the best of us are liable to become the victims of absurd illusion if we habitually allow our imaginations to be overheated, whether by furious passion or by excessive indulgence in the pleasures of day-dreaming, or in the intoxicating mysteries of spiritualist _seances_.

But if we take care to keep our heads cool and avoid unhealthy degrees of mental excitement, we need not be very anxious on the ground of our liability to this kind of error.

As I have tried to show, our most frequent illusions are necessarily connected with something exceptional, either in the organism or in the environment.

That is to say, it is of the nature of illusion in healthy conditions of body and mind to be something very occasional and relatively unimportant.

Our perceptions may be regarded as the reaction of the mind on the impressions borne in from the external world, or as a process of adjustment of internal mental relations to external physical relations.