Method XI yi 



Then replace 50 per cent, alcohol with distilled water. 



When the stain is cool enough (too great heat will injure the 

 celloidin sections), withdraw the water and pour the warm stain 

 over the sections, and set aside for 6-24 hours. 



The sections are now colored a deep brown-black. 



6. To differentiate. — Wash the sections in several changes of 

 tap water. This removes the surplus stain and, tap water being 

 alkaline in reaction, converts the color into a blue-black. If 

 found necessary, a few drops of a saturated solution of lithium 

 carbonate (see formula B) may be added to the water to hasten 

 the removal of the surplus stain and to produce the blue reaction. 

 Wash out the lithium carbonate with fresh water. 



The sections are now ready to be decolorized. 



Place three watch-glasses or shallow dishes on a white sur- 

 face. In the first pour a thin layer of the potassium permanga- 

 nate solution (C, i); fill the second with distilled water and the 

 third with the oxalic acid-potassium sulphite mixture (C, 2). 

 Have handy a larger vessel of distilled water. 



With section lifter and small forceps place the sections, one 

 or two at a time, in the permanganate solution until the gray sub- 

 stance can be clearly distinguished from the white as a dark 

 yellowish brown. While this usually occurs in 20-30 seconds, 

 it may take several minutes. 



Next wash in the distilled water for 2-5 minutes, and then 

 transfer to the oxalic acid-potassium sulphite mixture. Let remain 

 in this till the gray substance becomes a light yellowish-brown 

 and the white substance a light steel blue. This usually occurs in 

 less than i minute, but for thick sections or over-hardened mate- 

 rial it may take a longer time. 



After differentiation the sections are transferred immediately 

 to a large amount of distilled water for several minutes, and then 

 they may be placed in tap water, in which the blue color will 

 deepen slightly. It is essential that all the differentiating fluid 

 be washed out. ThisTnay be accomplished in 15-20 minutes, the 

 water frequently changed, but it does not injure the sections to 

 remain in water several hours. 



Digitized by Microsoft® 



