LESSON XXVII. 

 VISION. 



Accommodation. 



1. Remove very carefully the sclerotic and choroid 

 from a small portion of the posterior surface of 

 the eye of an ox or a sheep. Place the eye 

 in the end of a blackened tube just large 

 enough to hold it, with the cornea outwards. 



On looking through the tube at any object, the 

 inverted image will be seen shining through the 

 retina. 



Or, 



The eye of any small animal, e.g. rat, may be 

 used without any preparation, the sclerotic 

 being sufficiently thin to be transparent. It 

 will be found convenient to place the eye, with 

 the cornea downwards, on the stage of a micro- 

 scope, and to direct light through it by means 

 of the mirror. 



2. Standing some feet before a window, close one 

 eye and hold up before the other, at a distance 



