1895.] MICROSCOPICAL JOURIS'AL. 385 



lately necessary to combine many proceedings intended 

 to obtain a faithful fixation and a proper hardening. 



Fixation. — The fixing solution should be very penetrat- 

 ing, for the tissues forming the different parts of the eye 

 are of very different consistence. These are membranes, 

 like the sclerotica and the cornea, which possess con- 

 siderable consistence, and are consequently but slightly 

 permeable by the fixing liquids. These two membranes 

 placed at the outside of the eye ball surround the other 

 parts and prevent the penetration of liquids into the in- 

 terior of the organ, and the fixing of the elements com- 

 posing the contents of the ball. It is necessary to soften 

 the sclerotica to allow the fixing liquid to pass more 

 rapidly. For this purpose we use acetic acid, added 

 to the fixing liquid. The latter is composed of chromic 

 acid, picric acid and, in some cases, of osmic acid. 



Aqueous solution of chromic acid (1 per cent), twenty- 

 five volumes; saturated aqueous solution of picric acid, 

 ten volumes; water sixty-five volumes. Add a few drops 

 of acetic acid. To fix the elements as perfectly as possi- 

 ble it is indispensible to add to the mixture two volumes 

 of 1 per cent osmic acid. 



Place the whole eye in the mixture, and in four or five 

 hours, when the ball has acquired a certain consistence, 

 cut it in two so that the section shall pass through the 

 optic nerve and the middle of the cornea. 



Hardening. — Transfer these hemispheres to water, and 

 leave them for three or four days to remove the picric 

 acid and the color produced by the picric and the chromic 

 acids. Then plunge them into MuUer's fluid or into alco- 

 hol. The eye should remain for at least two weeks in 

 Muller's fluid, after which wash carefully, and stain in 

 mass with borax carmine. If alcohol is used transfer 

 successively to the stain, then to alcohol at 40°, 60°, 80° 

 and 90°. Stain in mass ,by borax carmine. Imbed in 

 paraffin or in celloidin. 



