93 ANIMAL MECHANISM. 



if the sensorium become disordered by disease, it no 

 longer recognises the images or impressions transmitted 

 to it through the visual nerve. Thus it will be under- 

 stood, that the eye may labor, receive, and transmit a 

 miniature picture of all it perceives to the soul ; but, if there 

 is a derangement of that mass of mysteriously constructed 

 matter, filling the whole skull, which all experience de- 

 monstrates to be the seat of thought, no idea is excited. 

 On the other hand, when individuals suddenly lose their 

 sight, without materially injuring the optic nerve, they 

 sometimes dream of seeing. In this case, imagination 

 excites the nerve in such a peculiar and inexplicable 

 manner, as to call up the idea of vision. This nerve 

 being formed with exclusive reference to that function, in 

 the economy of animal life, any impression upon it will 

 excite a corresponding impression in the brain, and no 

 other. 



All creatures, from man downward, living on land, 

 have their eyes very similar in structure. The same 

 quantity of light that enables a man to see distinctly, will 

 also answer for a horse, an ox, and, indeed, most of the 

 domestic and graminivorous animals. A natural inference 

 would be, then, were it not otherwise known by dissection, 

 that all the parts entering into the composition of their 

 eyes, in order to produce the same effect as in man, were 

 of the same materials. 



In carnivorous animals, the original principle of vision 

 is preserved, but most curiously modified, according to 

 their habits and characters. Those that feed on herbage, 

 are commonly of social dispositions, feeding in companies 

 through the day, and quietly ruminating or sleeping 

 through the night. 



Those, on the contrary, that live by violence, preying 

 on'those they have slain, are generally solitary: they lie 

 in ambush, alone, watching for their victim ; and it is so 

 ordered, by the immutable laws of nature, that they slay 

 such as are more timid and helpless than themselves. In 

 order to accomplish this, with the greatest certainty, 

 carnivorous animals have the power of seeing in the 

 dark. 



Fishes, by a further modification of the original appa- 



