The Celloidin Method 121 



the stain is extracted from the celloidin, or at least until the celloidin 

 retains only a faint pinkish color. Wash in 70 per cent alcohol (not 

 acid) until the characteristic purple color of the haematoxylin replaces 

 the red due to the acid. Stain in eosin (preferably a 1 per cent solu- 

 tion in 70 per cent alcohol) for 2 to 5 minutes. Dehydrate in 95 per 

 cent alcohol for about 5 minutes. Absolute alcohol must not be 

 used, unless it is desirable to remove the celloidin matrix. Eyeleshy- 

 mer's clearing fluid (equal parts of cedar oil, bergamot oil, and car- 

 bolic acid) clears readily from 95 per cent alcohol. Mount in 

 balsam. 



If serial sections are necessary, arrange the sections upon a slide, 

 using enough 70 per cent alcohol to keep the sections moist, but not 

 enough to allow them to float. Cover the sections with a strip of 

 toilet paper, which can be kept in place by winding with fine thread. 

 After the sections have been stained and cleared, remove the excess 

 of clearing fluid by pressing rather firmly with a piece of blotting- 

 paper. Then remove the toilet paper and mount in balsam. 



With occasional slight modifications, we have used the method 

 as presented by Eycleshymer in his classes. Instead of the graded 

 series of celloidin solutions, we use a 2 per cent solution, which is 

 allowed to concentrate slowly by removing the cork occasionally, 

 or by using a cork which does not fit very tightly. The material 

 is imbedded when the solution reaches the consistency of a very 

 thick oil. If the material is to be cut immediately, we prefer to 

 imbed it and fasten it to the block at the same time. The blocks 

 should have surface enough to accommodate the objects, and should 

 be about } inch thick. White pine makes good blocks; cork is 

 much inferior. Place the block for a moment in ether-alcohol and 

 then dip into the 2 per cent celloidin the end of the block which was 

 left rough by the saw. With the forceps remove a piece of the 

 material from the thick celloidin and place it upon the block, taking 

 care to keep it right side up. Dip the block with its object first in 

 thick celloidin, then in thin, and after exposing to the air for a few 

 minutes drop it into chloroform, where it should remain for about 

 10 to 20 hours. It should then be placed in equal parts of glycerin 

 and 95 per cent alcohol, where it may be kept indefinitely. If the 



