Microscopy. 947 
equal measure of alcohol, never the reverse, and the mixture should 
be kept cool, otherwise the acid may attack the alcohol. In such 
an event the solution is rendered worthless, and, should the speci- 
mens be in it at the time, the heat generated by the reaction gives 
the acid such additional dissolving power that the sections are at 
once destroyed. A more efficient acid reagent is a mixture of equal 
parts hydrochloric and nitric acids. A 35 per cent. solution of this 
mixture in strong alcohol gives better results than the pure nitric 
acid at 50 per cent., and does not so readily attack the alcohol. 
Of the alkalis, weak ammonia, sodic hydrate, and potassic hydrate 
are most serviceable. The solids are to be preferred to the ammonia, 
since from them solutions of a definite strength can more easily be 
made. An aqueous solution of $ or } per cent. potassic hydrate 
has given the most satisfactory results. 
The method of using the depigmenting fluid is as follows. 
Unstained material is cut in paraffine; the ribbons are mounted on 
a slide with Schallibaum’s fixative ; when the sections are fixed, the 
araffine is removed with turpentine; the slide with the sections is 
then successively washed with alcohol of 98 per cent., 90 per cent., 
70 per cent., and so on, till a grade homogeneous with the depig- 
menting fluid is reached. Into a shallow white dish filled with the 
depigmenting fluid the slide is now gently lowered. Ina few seconds 
the pigment, dissolving, will be seen as a reddish cloud. ‘The process 
1s usually completed in less than a minute, and the slide is promptly 
transferred to a dish of clean water or alcohol and there gently 
rinsed, The sections are next stained by exposure to the dye ina 
shallow dish. After being sufficiently stained, they may be washed 
and mounted in glycerine, or, after the proper steps in dehydrating 
-e : clarifying, mounted in benzol-balsam or other mounting 
ium. 
The dyes which have been found the most serviceable are some 
of the carmines and hematoxylin. The aniline dyes have almost 
invariably 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 rhabdomes and the cell boundaries were most 
distinctly shown by Kleinenberg’s hematoxylin. A’ very faint col- 
a oration with this dye gave the best results for nerve-fibres. 
et For the isolation of the retinal elements two maceration fluids 
__Were used. A weak solution of chromic acid, as employed by Pat- 
retina, after the removal of the lens and surrounding tissue, was placed 
oy this treatment, 
