458 BOTANICAL GAZETTE [JUNE 
four grams to roo“, and so on, through the series. Synthol (Bausch 
& Lomb Optical Co., Rochester, N. Y.) is a better solvent of celloidin 
than is absolute alcohol, and when it is used two more grades of cel- 
loidin — 22 and 24 per cent.— may well be used.’ 
Transfer the blocks from absolute alcohol to the 2 per cent. solution 
celloidin. _ Seethatthe bottle is almost filled, then wire or clamp the stop- 
per firmly in place, and put the bottle on its side in an ordinary paraffin 
bath at 50° to 60° C. for twelve or eighteen hours. Then cool the 
bottle quickly in cold water, taking care that the water does not get 
into the bottle. Next pour out the 2 per cent. celloidin solution and 
replace it with the 4 per cent. solution. Proceed in the same way with 
this and all the following grades of celloidin, up to the most concen- 
trated, and when this grade is reached it is to be gradually thickened 
by adding a few chips of dry celloidin from time to time, until the 
mixture in the bottle is quite stiff and firm. With a pair of forceps 
the blocks are now to be pulled out of the bottle, each with a coat of 
celloidin adhering, and are to be put into a bottle of chloroform to 
harden for twelve hours. From this they are transferred to a mixture 
of equal parts of 95 per cent. alcohol and glycerin, where they should 
remain for a few days before cutting, and where they will keep for an 
indefinite period. The time given to the process of infiltration should 
in no case be shortened, except for very small objects. An increase of 
the time is often advantageous. 
V. Secttoning.—The sliding type of microtome is a necessity in the 
cutting of celloidin material. The best pattern is the Thoma, as 
recently adapted, at the suggestion of Dr. Jeffrey, for cutting hard 
tissues. The knife should be extremely hard, as supplied for this pur- 
pose by Jung of Heidelberg, and should be kept honed to a keen, 
smooth edge. It is best to grind and hone the knife with a back, in’ 
order that the edge may not be too thin. The blade of the knife should 
have a dip of about ten degrees in the holder, and should be set more 
or less obliquely to the line of motion, according to the nature of the 
material, so as to make a long sliding cut. All bearing surfaces should 
be thoroughly cleaned with ether and then flooded with the best qual- 
ity of oil each time the microtome is set up for use. The block of 
material, if very hard or large, is to be clamped in a special object- 
carrier (as supplied by Jung), in such a way as to give the desired plane 
of section. Smaller and softer objects may be cut on the ordinary 
2 The celloidin ig ee bai he used aeons and should be kept in bottles 
lying on their sides, d concentration of the solutions. 
