1894.] MICROSCOPICAL JOURNAL. 87 



EDITORIAL. 



The use of Formalin in Hardening and Fixing Tissues. 



— At the meeting of Jan. 9, 1894, of the Microscopical Society 

 of this city, Dr. W. W. Alleger demonstrated a method of pre- 

 paring tissues so as to show bacteria, the new feature of which 

 consisted in the use of formalin as hereinafter described. 



The tissue selected was from the lungs and liver of a guniea 

 pig dead of anthrax. It was hardened by immersion for 48 

 hours in a 10 per cent solution of formalin, dehydrated in 

 alcohol, cleared in chloroform and imbedded in paraffine. 

 Sections were cut on a B. and L. Microtome, attached to the 

 slide by means of gelatine fixative containing formalin, and after 

 the fixative had thoroughly dried they were passed through 

 turpentine to remove the parafiine, then into alcohol and finally 

 into water. They were now stained for 5 minutes in an aniline 

 water solution of gentian violet decolorized in a weak solution of 

 iodine (Grains method) dehydrated in alcohol, cleared in cedar 

 oil and mounted in balsam in xylol. A modification of the 

 method mentioned consists in the use of aniline oil slightly 

 tinted with eosine, in place of alcohol as a decolorizing agent. 

 Thus treated the bacteria are stained a deep purple, the nuclei 

 a light purple, the protoplasm a light rose and blood corpuscles 

 brown, the result bring a beautifully stained and clearly differ- 

 entiated mount. 



Dr. Alleger claimed that tissues prepared in this way are 

 superior to those hardened in alcohol in that there is much less 

 shrinkage, and stated that while he was aware that bacteriol- 

 ogists generally do not look upon the paraffine method with 

 favor he preferred it because of the freedom from the trouble of 

 immerson fluids and for the reason that the tissue can be kept 

 in blocks indefinitely and is always ready for cutting. He put 

 most stress, however, upon his method of fixing the sections to 

 the slide which is a modification of Dr. Gray's gelatine fixative 

 method. To a dram of 2 per cent solution, he adds 4 or 5 drops 

 of formalin. A drop of this mixture is placed upon the slide, 

 the section laid upon it and gentle heat (not enough to melt the 

 parafl&ne) applied. No matter how wrinkled the section it 

 floats out flat and as soon as this occurs the excess of fixative is 

 I drained off and the adherent portion allowed to dry, when the 



