their achromatism is affected.
132.
In cases of milky cataract, a very turbid crystalline lens causes the patient to see a red light. In a case of this kind, which was treated by the application of electricity, the red light changed by degrees to yellow, and at last to white, when the patient again began to distinguish objects. These changes of themselves warranted the conclusion that the turbid state of the lens was gradually approaching the transparent state. We shall be enabled easily to trace this effect to its source as soon as we become better acquainted with the physical colours.
133.
If again it may be assumed that a jaundiced patient sees through an actually yellow-coloured humour, we are at once referred to the department of chemical colours,