As to the cause of that extraordinary colour in the crow's eyes, one might say that it was merely the reflected red light of the level sun. We are familiar with the effect when polished and wet surfaces, such as glass, stone, and water, shine crimson in the light of a setting sun; but there is also the fact, which is not well known, that the eye may show its own hidden red--the crimson colour which is at the back of the retina and which is commonly supposed to be seen only with the ophthalmoscope. Nevertheless I find on inquiry among friends and acquaintances that there are instances of persons in which the iris when directly in front of the observer with the light behind him, always looks crimson, and in several of these cases the persons exhibiting this colour, or danger signal, as it may be called, were subject to brain trouble. It is curious to find that the crimson colour or light has also been observed in dogs: one friend has told me of a pet King Charles, a lively good-tempered little dog with brown eyes like any other dog, which yet when they looked up, into yours in a room always shone ruby-red instead of hyaline blue, or green, as is usually the case. From other friends I heard of many other cases: one was of a child, an infant in arms, whose eyes sometimes appeared crimson, another of a cat with yellow eyes which shone crimson-red in certain lights. Of human adults, I heard of two men great in the world of science, both dead now, in whose eyes the red light had been seen just before and during attacks of nervous breakdown. I heard also of four other persons, not distinguished in any way, two of them sisters, who showed the red light in the eyes: all of them suffered, from brain trouble and two of them ended their lives in asylums for the insane. Discussing these cases with my informants, we came to the conclusion that the red light in the human eye is probably always a pathological condition, a danger signal; but it is not perhaps safe to generalize on these few instances, and I must add that all the medical men I have spoken to on the subject shake their heads. One great man, an eye specialist, went so far as to say that it is impossible, that the red light in the eye was not seen by my informants but only imagined. The ophthalmoscope, he said, will show you the crimson at the back of the eye, but the colour is not and cannot be reflected on the surface of the iris. Chapter Sixteen: In Praise of the Cow