AND ARTHROPODS, 163 



The Lens. — The lens is best prepared for sections by either 

 sulphuric or picro-sulphuric acid. By the first reagent its shape is 

 best retained, and the lens itself is less liable to be drawn away 

 from the surrounding tissue ; the latter reagent, however, brings 

 out more sharply the configuration of the cells and allows a 

 better stain of the nuclei to take place. 



The Retinophom. — The retinophorse are well preserved by 

 nearly all the reagents ; but in sublimate, in picric acid, or in their 

 combinations, they become slightly granular, and remain so closely 

 packed that it is difficult to distinguish the cell boundaries. 

 Chromic acid, one-fifth per cent, for three or four days, contracts 

 the cells and gives preparations in which the boundaries and 

 general arrangement of the retinophorse are easily studied. 



Sections of the Eye. — In order to obtain the best sections of 

 the adult eye with all the parts in the most natural position, it is 

 necessary to treat them first with one-tenth per cent, of chromic 

 acid for half an hour, then in one-twentieth per cent, for twenty- 

 four hours; one-tenth per cent, for twenty-four hours ; and finally 

 one-fifth per cent, for forty-eight hours or more. Next to this 

 method, it appears that solutions of sulphuric acid (twenty drops 

 to fifty grammes of water) give the best preparations (for 

 sectioning), of everything except the rods. 



The double layer of the sclerotica and the fibres penetrating it 

 can be seen in sections of eyes treated twenty-four hours in one- 

 fifth per cent, chromic acid. 



Maceratioii and Dissection. — -The pigmented epithelial cells of 

 Pecten's eyes and the cells of the cornea are easily isolated by 

 treatment with Miiller's fluid or bichromate of potash one-half per 

 cent, for two or three days. For the maceration of all other 

 elements weak chromic or sulphuric acid is used. For the outer 

 ganglionic cells, which are very difficult to isolate, maceration in 

 one-fiftieth per cent, chromic acid gives excellent results, after 

 previously fi.xing the tissue in one-fifth per cent, for a few minutes. 



For the retijiophorce., one-twentieth per cent, for four or five 

 days proves very useful. 



Sulphuric acid, five drops to thirty grammes of sea-water, gives 

 the best results for the nerve-endings in the retinophora^ (not in 

 the rods) and for the nervous inner prolongation of the outer 

 ganglionic cells. 



