ANIMAL MECHANISM. 105 



may be distinctly felt to slide upon each other, between 

 the thumb and finger. 



Little glands, like bags of oil, only to be seen by the 

 most powerful microscope, are lodged under the first 

 plate, which are continually oozing out their contents 

 upon the surface, which gives the sparkling brilliancy t^ 

 this part of the eye. As death approaches, this flu- 

 forms a pellicle, like a dark cloud, over the lower portion 

 of the cornea. This formation is taken to be a sure indi- 

 cation of approaching dissolution. Many diseases are 

 peculiar to the cornea ; such, for example, as a milky 

 colored effusion of matter under the external plate, pre- 

 venting a free transmission of light to the interior. See 

 fig. 2, letter d, and fig. 3, letters c and d, for representa- 

 tions of the cornea. 



By looking into a person's eye, there seems to be a 

 vertical partition, either black, blue, or hazle, as the case 

 may be, which prevents us from looking into the concealed 

 regions beyond, having a round hole in its centre. 

 Scientifically, this partition is called the iris, while its 

 central orifice is denominated the pupil How the diam- 

 eter of this hole is enlarged or diminished, anatomists 

 have never been fortunate enough to explain, satisfac- 

 torily, the apparatus is so minute, that they cannot decide 

 upon its true character. One fact, however, is certain, 

 that the pupil is large or small, according to the quantity 

 of light that may be necessary to the formation of a dis- 

 tinct picture of the object seen, and this change is 

 effected without our being conscious of the action. 

 Resembling other delicate membranes, in many respects, 

 we are unwilling to confuse the subject with a descrip- 

 tion that would distract the mind of a new beginner. 



From the reflection of such rays as are not admitted 

 through the pupil, or central hole, we account for much 

 of the lively brilliancy of the iris. On its back side it is 

 rather fleecy, like the tapetum, but dissimilar in other 

 respects. Over this is spread a black, blue, hazle, or tea- 

 colored paint, which gives a permanent color to the eye 

 It has been often remarked, that the eyes and hair ordi- 



