The destruction of sight, wherever the injuries be sustained, follows the same law: all colours are affected in the first place, and lose their saturation. Then the spectrum is simplified, being reduced to four and soon to two colours; finally a grey monochrome stage is reached, although the pathological colour 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’.