I have now to complete this statement by the observation that total forgetfulness of any period or stage of our past experience necessarily tends to a vague kind of hallucination.

In looking back on the past, we see no absolute gaps in the continuity of our conscious life; our image of this past is essentially one of an unbroken series of conscious experiences.

But if through forgetfulness a part of the series is effaced from memory, how, it may be asked, is it possible to construct this perfectly continuous line?
The answer is that we fill up such lacunae vaguely by help of some very imperfectly imagined common type of conscious experience.

Just as the eye sees no gap in its field of vision corresponding to the "blind spot" of the retina, but carries its impression over this area, so memory sees no lacuna in the past, but carries its image of conscious life over each of the forgotten spaces.
Sometimes this process of filling in gaps in the past becomes more complete.

Thus, for example, in recalling a particular night a week or so ago, I instinctively represent it to myself as so many hours of lying in bed with the waking sensations appropriate to the circumstances, as those of bodily warmth and rest, and of the surrounding silence and darkness.
It is apparent that I cannot conceive myself apart from some mode of conscious experience.