ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 673 



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 RetinopJiorse. — 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 1/5 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. 



Section of (lie 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 1/10 per cent, of chromic acid for half an hour, then in 1/20 per 

 cent, for twenty-four hours; 1/10 per cent, for twenty-four hours, and 

 finally 1/5 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 1/5 per cent, chromic 

 acid. 



Maceration and Dissection. — The pigmented epithelial cells of Pectens" 

 eyes and the cells of the cornea are easily isolated by treatment with 

 Miiller's fluid or bichromate of potash 1/2 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 1/50 per cent, chromic acid gives excellent results, after 

 previously fixing the tissue in 1/5 per cent, for a few minutes. 



For the retinophorse, 1/20 per cent, for four or five days proves very 

 useful. 



Sulphuric acid 5 drops to 30 grammes of sea-water gives the 

 best results fur the nerve-endings in the retinophorae (not in the rods), and 

 for the nervous inner prolongation of the outer ganglionic cells. 



In order to isolate pieces of the cornea with the subjacent pseudocornea 

 and the circular fibres on the outer surface of the lens, it is better to 

 macerate the eyes in sulphuric acid as given above. The same treatment 

 retains to perfection the natural shape of the lens, which may then be 

 isolated, and its surface studied to advantage. 



It is necessary for the study of the circular retinal membrane, the 

 septum, and the retina itself, to isolate the latter intact. Maceration in 

 chromic acid either makes the retina too brittle or too soft, while the axial 

 nerve-fibres remain so firmly attached to the retina that it is difficult to 

 isolate it without injury. But this may be easily and successfully done by 

 maceration for one or two days in the sulphuric acid solution. By this 

 treatment the retina, together with the septum and circular retinal membrane, 

 may be detached entire. 



Surface views of the retina show the peripheral outer ganglionic cells. 

 The argentea may be very easily separated in large sheets by macerating 

 for four or five days in bichromate of potash of 1 per cent. 



Sulphuric acid is a most valuable macerating as well as preservative 

 reagent. In weak solutions (40 drops to 50 grammes) entire molluscs, 

 without the shell, have been kept in a perfect state of preservation for more 

 than six months. For cilia and nerve-endings it is exceptionally good. 



The eyes of Area and Pcctunculus may be macerated either in Miiller's 



