176 BULLETIN OF THE 



given poor results. For general purposes Grenacher's alcoholic borax- 

 carmine is excellent. In both embryonic and adult material Czoker's 

 alum-cochineal gave fine nuclear outlines. In the adult eyes, the rhab- 

 domes and the cell boundaries were most distinctly shown by Kleinen- 

 berg's haematoxylin. A very faint coloration with this dye gave the best 

 results for nerve-fibres. 



For the isolation of the retinal elements two maceration fluids were 

 used. A weak solution of chromic acid, as employed by Patten ('86, pp. 

 736, 737), gave good results ; but since the mycelium of a fungus is often 

 developed in very dilute solutions of this reagent, it can be used only 

 when it is carefully watched and its results are controlled by another 

 method. It was employed in the following manner. The retina, after 

 the removal of the lens and surrounding tissue, was placed for five or ten 

 minutes in a ^% solution. After this treatment, which slightly hardened 

 the tissues, the first solution was replaced by a second of 5^0%- I" ^^is 

 the retina remained for three or four days, at the end of which time the 

 retinal cells were easily separable. The most satisfactory method of iso- 

 lating the cells is to place on a slide in dilute glycerine a small portion of 

 the macerated retina, and, having protected it with a cover-glass raised 

 on wax feet, to gently tap the cover-glass till the cells are separated. 

 One part of 0.2% solution of acetic acid in sea-water mixed with an 

 equal volume of 0.04% osmic acid in sea- water, although only partially 

 successful as a maceration fluid for the retina in scorpions, is a reliable 

 check for the results obtained from chromic acid. 



After the cells have been isolated, the abundance of pigment which 

 they contain so obscures their contents that scarcely more than their out- 

 lines can be studied. The removal of the pigment is on the whole more 

 successfully accomplished before than after isolation. For this process, 

 as for simple isolation, the retina should be subjected to the action of 

 ^% chromic acid for five or ten minutes, and then transferred to a solu- 

 tion of ^% potassic hydrate. In this the pigment dissolves, forming a 

 reddish cloud. After about a minute the retina should be removed to 

 distilled water, rinsed, and transferred to Grenacher's alcoholic borax- 

 carmine. This reagent performs both the office of a maceration fluid and 

 a dye. In from twelve to twenty-four hours the retinal cells can be iso- 

 lated, and present in difl'erent regions of the retina three principal condi- 

 tions. First, those from the exterior of the retina are seriously altered 

 by the continued action of the potash ; second, those from the centre of 

 the retina remain almost unchanged, still retaining most of their pig- 

 ment; third, those from an intermediate position, without being other- 



