1904] BRIEFER ARTICLES 459 
object-carrier. The object-holder in the latter instance consists of a 
tube of thin metal, plugged with hard wood. The end of this wooden 
plug is thoroughly coated with celloidin by dipping it repeatedly in 
4 per cent. celloidin and drying in the paraffin bath. The block of 
material is attached to this holder by means of a drop of the 4 per 
cent. celloidin. One face of the block must be trimmed flat and freed 
from glycerin before applying it to the moistened surface of the 
holder. It will set firmly in a few minutes. Run the carrier slowly up 
the ways by means of the feed-screw, cutting off the celloidin and 
trimming the block to the desired level. Do not cut thick pieces from 
the block with the microtome knife, as the latter is very apt to be 
injured in this way. Adjust the feed-mechanism to give the desired 
thickness, and then with a camel’s-hair brush flood the knife with go 
per cent. alcohol, and, holding the brush lightly on the top of the 
object, float the section out upon the knife. A slow, steady stroke of 
the knife generally gives the best results. The section is then removed 
from the knife by means of the brush, and is to be kept in 90 per cent. 
alcohol until needed for the next step in the process. The thickness 
of the section must depend upon the purpose for which the sections 
are made. For ordinary study with the microscope, 10pm is usually 
quite thin enough, but for photomicrography it is often desirable to 
have sections as thin as 5m or even less. 
VI. Staining and mounting.— To prepare the sections for staining 
_and mounting, it is usually most convenient to remove the celloidin at 
once by placing the sections for ten or fifteen minutes in ether, then 
wash in 95 per cent. alcohol, after which they may be transferred to 
water, stained, cleared, and mounted in the usual way. One of the 
most useful stains is the haematoxylin-safranin double stain. First 
stain the sections to a fairly dense purple in an aqueous solution of 
Erlich’s haematoxylin; wash in dilute aqueous solution of calcium or 
sodium carbonate, and then in two changes of distilled water. Adda 
few drops of alcoholic solution of equal ‘parts of Griibler’s alcoholic 
and aqueous safranin, and stain to a richred. A fairly dilute stain 
acting for one or two hours will give better results than a more con- 
centrated stain acting for a shorter time. ‘Transfer the sections directly 
to absolute alcohol, dehydrate rapidly, and transfer to xylol, benzol, 
or chloroform, and mount in Canada balsam (which has been pre- 
viously thoroughly dried) dissolved in xylol, benzol, or chloroform. 
Sections should be cleared in the same kind of liquid as is used for 
dissolving the balsam in which they are to be mounted. 
