BULLETIN OF THE UNITED STATES FISH COMMISSION. 207 



cut sections with the microtome, the method of imbedding was aban- 

 doned altogether. The thick blocks or slices were entirely freed from 

 alcohol by soaking in water for a day ; then removed, after drying them 

 off as much as possible with blotting paper or a soft linen cloth, to a 

 thick solution of gum arabic, in which it is best to allow them to remain 

 twenty-four to forty-eight hours so as to be thoroughly saturated. The 

 superfluous gum may then be poured off and the blocks of tissue, soaked 

 as they are with the gum, covered with strong alcohol. In twenty-four 

 hours the blocks will be found hard enough to cut. The blocks of hard- 

 ened tissue are simply held between the thumb and forefinger, and the 

 sections made with a section-knife with the free hand. When cutting 

 sections, it is necessary to keep the knife well wetted with alcohol so 

 that the sections may readily slide off on the upper side of the blade. 

 Water should not be used to wet the knife, as it would get on the block 

 of tissue, dissolve the gum, and soften the surface to be cut, and injure 

 the succeeding sections. The sections are lifted from the knife as fast 

 as cut, with a camel's hair pencil, and thrown into a dish of water, in 

 which the gum will dissolve out in a few minutes. The sections are 

 then ready to be stained, and in order to clearly differentiate the her- 

 maphroditic character of the reproductive glands of ostrea edulis a special 

 staining reagent must be used. The one which gives the best results 

 and acts most quickly will be given here. Equal parts of dense alco- 

 holic solutions of safranin red and methyle green * are poured together 

 and diluted with about eight times their combined volumes of water, 

 producing a dark purplish solution of about the color of claret wine. 

 Into this the sections may be thrown and allowed to remain until com 

 pletely saturated with color or until they are opaque; they may remain 

 in the staining fluid from one hour to a day, but two or three hours is a 

 sufficient length of time. When removed from the staining fluid they 

 are too deeply stained to be mounted at once, and must therefore be 

 transferred to 95 per cent, or absolute alcohol and stirred about in it 

 until the safranin red is no longer given off in clouds from the sections; 

 but it is important to note that if the sections remain in the strong alco- 

 hol too long the whole of the safranin will be washed out. In order to 

 prevent this, when it is seen that the section has acquired a rosy red 

 hue, combined with a bluish-green tint in the parts stained by the me- 

 thyle green, the object should at once be removed from the alcohol and 

 thrown into oil of cloves and mounted in balsam or daraar. The extrac- 

 tion of the superfluous color requires from five to fifteen minutes, ac- 

 cording to the thickness and character of the section, and should on no 

 account be allowed to proceed too far; if it does, the peculiar and im- 

 portant staining effect of the safranin is lost. As first pointed out by 

 Flemming, it has the peculiar property of staining the nucleus and its con- 

 tents, while it may be totally removed from other parts of the cell ; in 



* These are both aniline colors; the first is hard to obtain, except from dealers in 

 dyers' colors. 



