LIGHT AND DARK ADAPTATION
As an example of the general adaptation of the eye mentioned at the beginning of this article, observation shows that the eye is able to adapt itself to very different degrees of intensity of light.75 The investigations of the twentieth century have increased knowledge concerning light and dark adaptation greatly, although many questions are not yet solved.
The method of measuring the degree of general adaptation consists in the observation of an uncolored field of a definite size which can be illuminated by different intensities of light. The range of these intensities is great. Many forms of apparatus have been constructed ; one of the best seems to me to be that of Nagel.48 The intensity measurable can be varied from unity to 8,000,000.
The subject first studied is normal and pathologic dark adaptation, although light adaptation also shows individual differences and perhaps