THE EYE. 247 



allowing the vitreous humor to fall away from the 

 retina, into 2 per cent, solution of osmic acid, and 

 the anterior part into Miiller's fluid. The cornea 

 is to be cut through at one place with a sharp scalpel, 

 so that the preservative fluid may get freely into 

 the anterior chamber. 



The piece in osmic acid is left there for eight 

 hours ; it is then placed in water for two hours, and 

 finally transferred to a mixture of equal parts of 

 glycerine, alcohol, and water ; in this it is to remain 

 for a week or more, until wanted. 



The other piece is to lie in Miiller's fluid a fort- 

 night, changing the fluid one or twice ; it is then 

 placed in water for two or three hours, then 'in weak 

 spirit for a day or two, and finally preserved in 

 strong spirit. Of the lower animals, the eyes of the 

 pig serve best for exhibiting the minute structure, 

 especially of the retina. In this animal the eye 

 corresponds more closely in point of size, and ap- 

 proaches more nearly in structure to the human eye 

 than that of the ox or sheep, the other animals the 

 eyes of which are usually readily procurable. 



Preparation 1. The eyelids. These are studied 

 by making sections of the hardened lid across its 

 long axis and vertically to its surfaces. The lid 

 may be obtained from a still-born child, preferably 

 one the bloodvessels of which have been injected. 

 It is to be hardened in spirit and embedded, and 

 the sections which present no unusual difficulty 

 stained with logwood and mounted in dammar. In 

 this way almost all the parts are well displayed ; 

 the skin with its epidermis on the outer side, and 

 with a few small hairs and sweat glands seen here 

 and there; the mucous membrane (conjunctiva) on 

 the inner side ; the Meibomian glands cut along the 

 length of their wide, straight duct, with their round 

 saccules lined with epithelium cells (of a whitish 

 glistening appearance, due to the fatty secretion 

 they contain, and which also fills the duct); the 

 eyelashes with their large hair-follicles and seba- 



