88 THE SENSORIAL FUNCTION. 



ing rays of light which might dazzle and confuse. The black paint, pigmentum 

 nigrum, seems perfectly to discharge this function in the human eye. It is placed 

 immediately under the retina or expansion of the optic nerve. The rays of light fall 

 on the retina, and penetrating its delicate substance, are immediately absorbed or 

 destroyed by the black covering of the choroides underneath. For the perfection of 

 many of his best pleasures, and particularly of his intellectual powers, man wants 

 the vivid impression which will be caused by the admission of the rays of light into 

 a perfectly dark chamber; and when the light of the sun begins to fail, his superior 

 intelligence has enabled him to discover various methods of substituting an artificial 

 day, after the natural one has closed. Other animals, without this power of kindling 

 another, although inferior light, have far more to do with the night than we have. 

 Many of them sleep through the glare of day, and awake and are busy during the 

 period of darkness. The ox occupies some hours of the night in grazing; the sheep 

 does so when not folded in his pen ; and the horse, worked during the day for our 

 convenience and profit, has often little more than the period of night allotted to him 

 for nourishment and repose. Then it is necessary that, by some peculiar and adequate 

 contrivance, these hours of comparative or total darkness to us should be partially 

 yet sufficiently illuminated for them ; and therefore in the horse the dark brown or 

 black coat of the choroides does not extend over the whole of the internal part of the 

 eye, or rather it is not found on any part on which the rays proceeding from the 

 objects could fall. It does not occupy the smallest portion of what may be called the 

 field of vision ; but, in its place a bright variegated green is spread, and more over 

 the upper part than the lov/er, because the animal's food, and the objects which it is 

 of consequence for him to notice, are usually below the level of his head — thus, by 

 suffering the impression to remain longer on the retina, or by some portion of light 

 reflected from this variegated bed on which the retina reposes, or in some other inex- 

 plicable but efficient way, enabling the animal, even in comparative darkness, tc 

 possess the power of vision equal to his wants. 



The reader may see in the dusk, or even when duskiness is fast yielding to utter 

 darkness, the beautiful sea-green reflection from the eye of the horse. It is that 

 lucid variegated carpet of which we are now speaking. 



Who is unaware that in the fading glimmering of the evening, and even in the 

 darker shades of night, his horse can see surrounding olijects much better than his 

 rider; and who, resigning himself to the guidance of that sagacious and faithful 

 animal, has not been carried in safety to his journey's end, when he would otherwise 

 have been utterly bewildered ] 



If the reader has not examined this beautiful pigment in the eye of the horse, he 

 should take the earliest opportunity of doing so. He Avill have a beautiful illustration 

 of the care which that B^'ing who gave all things life has taken that each shall be 

 fitted for his situation. The iiorse has not the intelligence of man, and may not want 

 for any purpose of pleasure or improvement the vivid picture of surrounding objects 

 which the retina of the human being presents. A thousand minute but exquisite 

 beauties would be lost upon him. If, tiiereforc, his sense of vision may not be so 

 strong during the day, it is made up to him by the increased power of vision in thft 

 night. 



Perfectly white and cream-coloured horses have a peculiar appearance of the eyes. 

 The pupil is red instead of black. There is no black paint or brilliant carpet. It is 

 the choroid coat itself which we see in tliem, and not its coverinrr; and the red 

 appearance is caused by the numerous blood-vessels which are found on every part 

 of that coat. 



When we have to treat of other domestic animals, we shall see how this carpet is 

 varied in colour to suit the situation and necessity of each. In the o\- it is of a dark 

 green. He has not many enemies to f(>ar. or nnicli difficulty in searchino" fcr nourish- 

 ment, and the colour of tho ej'e is adapted to his food. In the eat and all his varieties, 

 it is yellow. We have heard of the eyes of the lion appearing like two flaming 

 torches in the night. Tiiere are few of our readers who iiave not seen the same 

 singular glare from the eyes of the domestic oat. In the wolf, and likewise in the 

 dog, who, in his wild state, prowls chiefly at nijht, it is grey. In tiie poor unjustly- 

 persecuted badger, who scarcely dares to crawl forth at night, although sheltered by 



