il893-] NEW-YORK MICROSCOPICAL SOCIETY. 51 



Dr, Carl Heitzmann replied to certain statements of Dr. Julien, 

 on the uses of acid preservatives, as follows: 



" The essayist has spoken rather slightingly of certain acids 

 and their dilute solutions as preservative fluids. Still there is 

 nothing better for the preservation of both animal and vegetable 

 tissues than a half of one per cent solution of chromic acid. 

 Sections through any portion of the pldnts will be preserved, with- 

 out noticeable change, by being dipped into the named solution 

 for one or two hours. The most delicate animal tissues, such as 

 chick embryos, from the very beginning of development, can be 

 preserved by being kept first in a one-tenth of one per cent so- 

 lution of chromic acid, gradually being transferred to stronger 

 solutions, never exceeding one-half of one per cent. 



" The brain, spinal cord, the eyeball, and especially the retina 

 are best preserved in Miiller's fluid, consisting of one per cent bi 

 chromate of potash, two per cent sulphate of soda, and ninety- 

 seven per cent distilled water. This fluid preserves admirably, 

 though it hardens but slowly. Alcohol may be in turn resorted to 

 for the latter purpose. The preservation in alcohol alone is ob- 

 jectionable for microscopical purposes, on account of pronounced 

 shrinkage and abstraction of color. 



" Another excellent preservative fluid is a one to two per cent so- 

 lution of osmic acid, which keeps the minutest structural features 

 unchanged, even in the most delicate (nerve) tissues of animal 

 organisms. Theo. Eimer, of Tubingen, has succeeded in preserv- 

 ing, by means of osmic acid solutions, evcn the most minute 

 structures of jelly-fish, transferred directly from sea water to the 

 solution. I have specimens of the retina and the spinal cord of 

 man and rabbit, perfectly preserved by osmic acid solution for a 

 number of years. 



*■ As regards mounting media, I concur with the essayist in the 

 statement that we are lacking perfection. The worst used is Can- 

 ada balsam, strictly objectionable because clearing up the spe- 

 cimens far too much. For the last twenty years I have used 

 nothing but chemically pure glycerin of Merck in Darmstadt, Ger- 

 many, which, though expensive, yields excellent results. Of course 

 great skill is needed for finding the proper amount of glycerin to 

 fill the space between slide and cover glass. The slightest sur- 

 plus, oozing forth at the borders of the cover glass, must be re- 



