xxix] EYE 227 



or longer ; then the lens is cut out with its capsule, and 

 vertical sections made through its centre with a freezing 

 microtome ; neither the lens nor the sections should be touched 

 with spirit. 



The lens fibres may be to a certain extent isolated by placing 

 for a day in 33 p.c. alcohol. 



Posterior part of eye of newt or other small animal. The eye is 

 suspended in osmic acid vapour for 10 minutes, placed in 

 Flernming's fluid for about 2 hours, the anterior part removed, 

 the posterior part passed slowly through alcohols, and imbedded. 

 Sections stained on the slide with Ehrlich-Biondi fluid. 



Retina. The treatment by the Golgi method is chiefly due 

 to Ram6n y Cajal. The retina is removed, then 



(a) rolled up, dipped for a second in dilute celloidin 

 solution, and exposed to the air for a second to allow the solution 

 to acquire a little consistency, 



or (>) the vitreous humour side is covered with a thin layer 

 of gelatine, 



or (c) the retina is simply removed from the eye. 



It is then placed for 

 1 2 days in Golgi's mixture (p. 247) ; then the fluid adhering to 



it removed with blotting-paper. 

 1 2 days in '75 p.c. silver nitrate ; the excess of fluid removed 



as before. 

 1 2 days in Golgi's mixture, but containing only to the 



amount of osmic acid. 

 1 2 days in '75 p.c. silver nitrate. 



It is then treated as other Golgi preparations, cp. p. 240. 



The celloidin or gelatine is used to avoid the precipitate 

 of silver salts which is apt to form in the outer part of thin 

 tissue. According to Ram6n y Cajal it is best to take the retina 

 of a large animal. 



The methylene-blue method is chiefly due to Dogiel. It is 

 similar to that given above for nerve-endings (Less. xvi.). The 

 retina is placed on a slide, vitreous humour surface uppermost, 



152 



