The courier-index., 1920-06-25
WHY THE CAT CAN SEE (By Garrett P. Serviss)


 "Would you kindly set me straight on three questions? 1. Can a cat see better or see at all in the dark? l2 Can a bat see in the dark? Can deep sea fish see?-J. L."
 Your questions involve some very interesting points in natural his tory. Let us take them up in order.
 |. Cats unquestionably can see well in the dark, but whether they can see better in the dark than in the light is something that per haps, could only be definitely de- termined by themselves. Inasmuch as most of their hunting for food seems to be done at night it is reasonable to assume that they can see at least as we'll by night as by day.
 If you examine the eyes of cat and experiment. a little with the ef- fleets that variations of illumina- tion plainly produce upon them, you will quickly become acquainted with the mechanism by means of which cats are able to see we'll both by day and by night This mechan- ism consists in a very sensitive au- tomatic control of the muscles which govern the width of the opening in the iris, called the pupil. The amount of light entering the eye and effecting the optic nerve, of course, depends upon the size or width of the opening.
 In the hun,ap ava tho pupil iS round and it's variations of size m accordance with changes of il- umlnation resemble those of the IT'S dlaphram" of a camera. The outline IS always round, whether .ne opening. be large or small. But 1ae pupil of cats eye, like that or the eyes of all nocturnal ami mais, changes from a more or less tounded out line when it is fully opened to a narrow eclipse, becom
 lg m the extreme a mere vertical slI when the opening is diminished. .H mas been thought that yer acai slit may be peculiarly adapted the perception of feeble light, slnce not only carnivorous mammals nocturnal habits, have that form ol 2 pupil, but it is found also in 'ne eye of the owl.
 M bright light the cats eye Eupiis becomes hardly more than a n , snowlng how very sensitive the npSe m"ss nerve must be to light, much a Oie sensitive no doubt, than that s;.;.a human eye. The extra sen s,uyehess combined with the great cons. s. ol opening of the pupil ac- ssun1s sSe Tor the ability of the cat to nish. % equally we'll by day and by tb.. That does not imply however, sias ehe cat can see in absolute aA. tSa It only implies as just said, sansi.: an ieAistence of a great degree of tba b,s;iveness ";s to feeble light. But be ona Snnple Tact that the pupil must tho VpeIed ed to its widest extent in conlS m uark proves that even the cat bowouuno bu not see without some light, | # mo' ei rant or even imperceptible, pans pc to our less sensitive or diff.. The case of the bat is quite nal leieht ' There we have an ami vss,, as, about whose organs of sense made extraordinary h statements are the may Dy haturalists. It is one of | "The ,Sels ot the animal kingdom. | bat membranous wings of the pedia writer in the "Encyclo- organ americana" ae "are not only an form foa. oa Tight, enabling it to per Exceeded m tHe air probably not | are also os any bird or insect, but | Creature means of informing the |
 SpallanasIo 10 It's surrounding" those of a,l istn experiments, and | ed that tba b1a'er naturalists, have prov organs d;s.n mInute and curious sense ! surface osS'LtlDuted os over the wing " instr,,nsoats pats are (perhaps main animal to mental ut; in enabling the complete dg wing their way through
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