“The destruction of sight, wherever the injuries be sustained, follows
the same law: all colors are affected in the first place,and lose their
saturation. Then the spectrum is simplified, being reduced to four and
soon to two colors; finally a grey monochrome stage is reached,
although the pathological color is never identifiable with any normal
one. Thus in central as in peripheral lesions ‘the loss of nervous substance results not only in a deficiency of certain qualities, but in the
change to a less differentiated and more primitive structure’.”