ELEMENTARY PHYSIOLOGY. [XXVJ. 



to 24 hours, as convenient; tease out in water 

 in dilute glycerine. Observe the isolated frag- 

 ments of the various layers, noting especially 



a. The large outer limbs of the rods, their 

 striation and transverse lamination. 



6. The pigment- cells, each consisting of a 

 colourless outer part, containing the nucleus, 

 and a coarsely pigmented part, which splits 

 up into a number of fibres, amongst which 

 are imbedded the heads of the rods. 



DEMONSTRATION. 



Effect on the iris of stimulating the sympathetic 



nerve. 

 Muscles of the eye dissected in the head of a 



sheep or dog. 



