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practical IHotee on Ibietoloo^. 



By V. A. Latham, B.Sc, F.R.M.S., F.S.Sc. 



Special Methods for Examination of the Eye. 



TO study the eye is one of the most difficult organs in this 

 work, it is so easily destroyed, difficult to manipulate to the 

 best advantage, requiring much judgment, care, and patience. If 

 possible, the human eye should be used, for there are some slight 

 differences in the structure of some of the parts of the eye in man 

 and animals, and moreover it is, I think, easier to demonstrate 

 this in the human eye. It is essential to obtain it in a perfectly 

 fresh condition, and on this account the difficulty is increased. 



Of the lower animals, the eyes of the pig and frog are best 

 for minute structure, especially the retina. For a general preser- 

 vative I use Miillers fluid, and when hardened wash well in water, 

 and then place in 2 parts spirit and i part water ; after one or two 

 days, not longer, place the eye in pure spirit till wanted. Another 

 way is, as soon after removal as possible, to separate the eye, by 

 an oblique cut with a very sharp knife or razor, into two halves — 

 an anterior and a posterior. The cut to start from must com- 

 mence just behind the attachment of the iris anteriorly and 

 superiorly, and pass downwards and backwards towards the 

 posterior part of the organ, coming out a little below the yellow 

 spot and optic nerve. Then place the posterior part, after allow- 

 ing the vitreous humour to fall away from the retina, into a 2 per 

 cent, solution of osmic acid and the anterior part in 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, 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 speci- 

 mens must ?iot be handled more than can be helped. 



The Eye-lids. — Make sections of the hardened lid across its 

 long axis and vertically to its surfaces. It is hardened in spirit or 

 Miiller embedded, cut, and the sections stained with logwood, log- 



