PHYSIOLOGY OF THE SENSE ORGANS. 



LESSON LX. 



FORMATION OF IMAGE DIFFUSION- 

 ABERRATION ACCOMMODATION - 

 SCHEINER'S EXPERIMENT NEAR AND 

 FAR POINTS PURKINJE'S IMAGES- 

 PHAKOSCOPE ASTIGMATISM. 



1. Formation of an Inverted Image on the Retina. 



(a.) Fix the fresh excised ox-eye provided for you, 

 remove the sclerotic from part of the posterior segment of 

 the eye near the optic nerve. Holl up a piece of blackened 

 paper in the form of a tube, black surface innermost, and 

 place the eye in it with the cornea directed forwards. Look 

 at an object e.g., a candle-flame and observe the inverted 

 image shining through the retina and choroid. 



(6.) Fix the fresh excised eye of an albino rabbit in du 

 Bois-Reymond's apparatus provided for you, and observe 

 the same phenomenon. The eye is fixed in with moist 

 modeller's clay. Observe the effect on the retinal image 

 when a convex or concave lens is placed in front of the 

 cornea. These lenses rotate in front of the cornea, and are 

 attached to the instrument. 



(c.) Focus a candle-flame or other object on the ground 

 glass plate of an ordinary camera for photographic purposes, 

 and observe the small inverted image. 



2. Diffusion. 



(a.) In a dark room place a lighted candle or gas burner 

 conveniently, and by means of a convex lens focus the 



