230 PRACTICAL NOTES ON HISTOLOGY. 



Bichloride of Mercury.— A freshly-opened eye is placed in a 

 saturated watery solution for three to six days, and finally hard- 

 ened in alcohol as before. Some were placed in alcohol 

 containing 2 per cent, of carbolic acid instead of simple alcohol. 

 The salt " fixed " in a manner much superior to Miiller, but 

 allowed shrinkage in the rod-layer. The fixing solution must get 

 access to the retina rapidly, and is accomplished by making an 

 incision one-fourth the length of the circumference of the eye, 

 and place at once in a fixing solution. At the end of thirty minutes 

 or less the posterior part of the eye was removed by enlarging the 

 original incisors with sharp scissors. By this means the fixing 

 agent obtained access to the retina rapidly, and the detachment of 

 the retina was prevented. 



Picric Acid.— A fresh and opened eye is placed in a saturated 

 watery solution of picric acid for three days, and the hardening 

 was then completed in alcohol and carbolic acid. It is not a 

 good agent except for showing the structure of the nervous 

 layers. It is also possible to trace the Miillerian fibres, at all 

 events as far as the reticular layer, since the previous immersion 

 of the retina in picric acid seems to intensify the eosinophilous 

 property which these fibres exhibit. 



Carbolic Acid. — Place a fresh-opened eye in a 2 per cent, 

 aqueous solution of the acid for a week; then harden in alcohol 

 as usual. The acid itself does not harden. Fair specimens of all 

 parts of the retina may be obtained thus. 



Zinc Chloride. — Place the eye in i per cent, watery solution for 

 a week and remove them to an alcoholic solution of carbolic acid. 

 The action is similar to picric acid as regards the Miillerian fibres, 

 but destroys the outer retinal layers. 



Permanganate of Potash.— Place the eye in 2 per cent, solution 

 for seven days. The alcoholic carbolic acid is not very satis- 

 factory. 



Chromic Acid.— Place the fresh-opened eye in one-sixth per 

 cent, watery solution and leave for twenty-four to forty-eight hours. 

 Finish hardening by alcohol and carbolic-acid solution. If left 

 longer than forty-eight hours, staining is difficult to accomplish. 

 It is very good for all parts except the rod-layer. 



