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Tissues of the Frog Tadpole's Tail. 
placed for three minutes in the usual iron developer with acetic acid 
employed for developing photographic negatives ; again washed 
with several changes of water, and mounted in a nearly saturated 
solution of acetate of potash slightly acid with acetic acid. 
This plan furnished beautiful results. The reason why the 
iron developer was used arose from finding that if the specimens 
after the logwood tincture were washed with our ordinary well 
water, which contains a little iron, they were greyer in tint than if 
washed in pure water. 
The same plan was modified by placing twice alternately after 
removal of the epithelium, into the chromic acid and sweet nitre 
mixture and diluted logwood tincture, without using the iron 
developer, and which gave fair specimens. 
No. 7 Method. — The same as No. 6 plan, only keeping the 
tadpoles in the chromic acid and sweet nitre mixture for forty minutes 
before removing the epithelium by the ammoniated water, and after 
its final removal very gently by the brush, rewashing and placing 
the specimens in the tincture of logwood first for five minutes ; then 
well washing and replacing in fresh chromic acid and sweet nitre 
for ten minutes ; again washing and mounting in the acetate of 
potash, as above. The specimens did not quite equal No. 6 plan. 
No. 8 Method. — Living tadpoles were placed for fifteen minutes 
in the chromic acid mixture, and well washed ; then the epithelium 
softened by the ammoniated water and removed under pure water, 
as above described ; again well washed and placed in “ Mordan’s 
purple ink ” diluted with two-thirds water for ten minutes (ink 
supposed to be made from aniline), well washed in water weakly 
acidified with acetic acid and mounted in acetate potash solution. 
This also gave beautiful preparations. 
The attempt to hurry the effects of the reagents by increasing 
their strength and diminishing the times did not yield equal results. 
The mixtures and the ammoniated water to be used fresh each time. 
Dead specimens, in which the fine nerve threads might be supposed 
to have considerably changed, did not under the microscope appear 
to have suffered in any way, save that the epithelium could be 
removed after a very brief immersion with ammoniated water. 
This plan may be found useful for some living structures, or such 
as are only recently dead. Instead of stripping the sides from each 
other, the central muscular portion of the tail, snipped off after 
preparation, is carefully removed by scissors under water, then the 
thin portions lifted out on a thin silver spatula, drained from the 
edge by blotting-paper, and gently pushed off into the mounting 
medium on the slide. If steel instruments be used they very 
quickly tarnish by the acetate potash and acetic acid, get slightly 
roughened, the delicate specimens cling to the surfaces, often 
become tom or doubled over, and thus they are somewhat difficult 
