PRACTICAL NOTES ON HISTOLOGY. 231 



Chloral Hydrate.— Put the fresh-opened eye in lo per cent, 

 solution for from two to seven days, complete in alcohol and car- 

 bolic acid. It is uncertain, but still occasionally gave first-class 

 results. It preserves the rod-layer, and it is possible sections may 

 be got with the rods and cones in situ. 



Gold Chloride, in various strengths, given above. Osmic and 

 chromic acid for from two to five days ; then in a neutral, slightly- 

 alkaline solution of the gold salt for thirty minutes. Transfer to 

 a solution of weak formic acid at a temperature of 30^ C, 86^ F. 

 in the dark ; after twenty-four hours the reduction is complete. 



Osmic Acid is about the most reUable re-agent, {a) Place the 

 fresh-opened eye for twenty-four to forty-eight hours (not longer) 

 in a watery solution of osmic acid, 10 per cent., and chromic acid 

 one quarter per cent. Then place in a mixture of alcohol and 

 carbolic acid for fourteen days or more. The retina is very hard, 

 but not brittle. The sections show the structure of all parts of the 

 retina, the rods being sharply defined and remaining in situ. 

 N.B. — It must be kept in solution no longer than forty-eight 

 hours, or it becomes brittle. 



ib) Place the fresh-opened eye in 075 to i per cent, solution 

 of osmic acid for from thirty minutes to twelve hours ; then treat 

 with either [a) alcohol, glycerine, and water ; {b) alcohol ; or {c) 

 alcohol and carbolic acid. 



{c) To obtain rapid penetration of the retina by the fixing 

 re- agent, solutions of osmic acid and chromic acid in alcohol were 

 employed :~(i) Osmic acid, one-tenth per cent. ; chromic acid, 

 one-fourth per cent. ; commercial alcohol and water, equal parts. 

 (2) Osmic acid, one-fifth per cent. ; chromic acid, one-sixth per 

 cent. ; commercial alcohol and water, equal parts. Good sections 

 were got with these except of the rod-layer. 



{d) Place the fresh-opened eye in a solution of osmic acid, 

 one-fifth per cent., and chromic acid, one-sixth per cent, (watery 

 solution) for twenty-four to thirty-six hours. Then transfer to 

 alcohol and carbolic-acid solution and treat as before. Excellent 

 results. 



Staining.— Retinal sections may be stained after being in cel- 

 loidin, but if embedded by the paraffin or cacao-butter method, 



