To this point I shall have occasion to return by-and-by.
I have now probably said enough respecting the illusions that arise through the fact of there being fixed limits to our sensibility.

The _rationale_ of these illusions is that whenever the limit is reached, we tend to ignore it and to interpret the impression in the customary way.
_Variations of Sensibility._ We will now pass to a number of illusions which depend on something variable in the condition of our sensibility, or some more or less exceptional organic circumstance.

These variations may be momentary and transient or comparatively permanent.

The illusion arises in each case from our ignoring the variation, and treating a given sensation under all circumstances as answering to one objective cause.
First of all, the variation of organic state may affect our mental representation of the strength of the stimulus or external cause.

Here the fluctuation may be a temporary or a permanent one.