336 Journal of Applied Microscopy. 



then add se\eral drops of distilled water and float the sections or ribbons on the 

 water. \\'arm gently until the paraffin becomes smooth and free from wrinkles. 

 Be careful not to melt the paraffin, for the albumen of the fixative coagulates 

 with less heat than is required to melt the paraffin. After the sections become 

 smooth remove the water with blotting paper and allow the slide to dr}-. The 

 drving will require two or three hours, and a longer period does no harm. 

 If the fixative is used alone, none of this dela}- is necessary since the sections are 

 merely laid upon the fixative and pressed down gently with the linger. 



10. Removal of the Paraffin. — To remove the paraffin it is ver}- customary 

 to heat the slide gently until the paraffin melts, and then place the slide in xylol 

 for thirt)- seconds or a minute. I believe, however, that it is far better to merely 

 warm the slide a little (not warmer than 30 degrees C.) Good xylol will then 

 remove the paraffin in two or three minutes. Even if the slide should not be 

 warmed at all, good xylol should remove the paraffin in five minutes. 



11. Removal of Xylol. — The xylol may be removed either by absolute alcohol 

 or bv the 95 per cent. The absolute alcohol does not seem to be really necessar}\ 

 For my own work I have two Stender dishes of xylol and two of absolute alcohol. 

 After the xylol has been used for a time I employ it only for removing paraffin, 

 and in the same way use the absolute alcohol only for removing the xylol, while 

 the other two dishes are used only for dehydrating and clearing. In transferring 

 from xylol to absolute alcohol, or vice versa, it is well to drain off the superfluous 

 liquid by resting the comer of the slide on a piece of blotting paper. These 

 rather expensive reagents will last much longer if this precaution is taken. 



12. Iransfer to the Stain. — Stains are aqueous or alcoholic, and alcoholic stains 

 are of various strengths. If an aqueous stain be used, the slide should be passed 

 successively through the alcohols 95 per cent., 85 per cent., 70 per cent., 50 per 

 cent., and 35 per cent., allowing each to act for about thirty seconds, after which 

 the slide is put into the stain. (In many cases it is sufficient to put a few drops 

 of the stain on the slide with a pipette.) From the stain the slide is passed back 

 through the various grades of alcohol, allowing it to remain about thirty seconds 

 in each as before. If the stain be alcoholic of about 70 per cent, strength, the 

 process is somewhat shorter, for the slide goes into the stain from 70 per cent, 

 alcohol, and goes back into 70 per cent, alcohol from the stain. The rule 

 is to transfer to the stain from the alcohol which is nearest the strength of the 

 stain. Exceptions to the rule \\\\\ be considered when treating of the various stains. 



13. Clearing. — After the sections have been stained, passed back through the 

 various grades of alcohol, and have been thoroughly dehydrated in absolute 

 alcohol, they are cleared or made transparent by means of xylol or some other 

 clearing agent. The clearing agent must be a solvent of balsam. From thirty 

 seconds to five minutes will be sufficient for clearing any kind of sections. 



14. Mounting in Balsam. — After the sections are cleared, wipe the slide on 

 the side which does not bear the sections. Put on a drop of Canada balsam and 

 add a clean, thin cover. Before you put the cover on, pass it through the flame 

 of an alcohol lamp to remove moisture, for it would be a pity indeed to injure a 

 preparation at this stage of the process. Add a label and the mount is complete. 



( To be Continued.) 



