468 Journal of Applied Microscopy. 



alcohols, since for accurate work these usually have to be renewed on account of 

 the coloration due to the stains, and not on account of any lack of effectiveness 

 in the alcohol itself. 



The figure represents fourteen staining dishes of a new pattern. The whole 

 group occupies a space of only six and one-eighth inches by three inches, and 

 each dish requires only 20 cc. of the reagent. Four slides may be stained at 

 a time by placing them back to back. The tops of the dishes are ground smooth, 

 and are covered by slips of ground glass (not shown in' the figure), one and 

 three-eighths of an inch long, and three-quarters of an inch wide. Although rather 

 tall and slender, the dishes will stand alone, but it is better to surround the 

 whole group by a strong rubber band. The interior of the dish is one and one- 

 eighth inches long, one-half inch wide, and three and one-quarter inches deep. 

 The bottom of the interior is not fiat, but broadly ^/-shaped. The economy 

 in space is an essential point, and the saving in reagents would soon pay for the 

 dishes. Chas. J. Chamberlain. 



University of Chicago. 



METHODS IN PLANT HISTOLOGY. 



Charles J. Chamberlain. 



VI. 



THE CELLOIDIN METHOD. 



" Celloidin is a form of nitro-cellulose." It is very inflammable, but does 

 not explode. It may be obtained in the form of tablets or cuttings, which have 

 to be dissolved in a mixture of equal parts of absolute alcohol and ether. It is 

 customary to use two solutions, a "thick" and a "thin." The thick solution 

 (about 10 or 12 per cent.) should have about the consistency of thick syrup. 

 The thin may be made by mixing equal parts of the thick and ether alcohol. 



As mentioned in the chapter on the General Method, the killing, washing, 

 and dehydrating are the same as for the paraffin method. After dehydrating in 

 absolute alcohol the succeeding steps are as follows : 



(1) Ether alcohol, 1 to 2 days. 



(2) Thin celloidin, 2 to 6 days. 



(3) Thick celloidin, 3 to 10 days. 



It seems better, however, to begin with about 2 per cent, celloidin and transfer 

 successively through 4 per cent., (3 per cent., etc., to 12 per cent., or to allow 

 the 2 per cent, to concentrate by removing the cork for a short time each day. 

 4. Imbedding. — The material may be imbedded and mounted upon a block 

 at the same time. The blocks should have surface enough to accommodate the 

 objects, and should be about one-fourth of an inch thick. Place the block for a 

 moment in ether alcohol and then in 2 per cent, celloidin ; 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 ten to twenty hours. It 



