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METHODS IN PLANT HISTOLOGY 
knife. A split or a scratch in the ribbon is often caused by some 
hard granule which becomes fastened to the inner side of the edge of 
the knife. This is the most common cause of the difficulty. Simply 
wipe the knife by an upward stroke of the finger, slightly moistened 
with xylol. Do not use a cloth. 
Sometimes good sections can be cut with a rather slow stroke 
when a rapid stroke fails. When paraffin is rather hard, sections 
may sometimes cut nicely at 5 when, at 10 n , ribbons cannot be 
secured. If very thin sections are desired and the paraffin seems 
too soft, cool the paraffin and the edge of the knife with ice, by Land’s 
cooling device, or by pressing a piece of ice against the paraffin block 
and the knife. Sometimes hard paraffin does not ribbon well. This 
difficulty may be remedied by dipping a hot needle in soft paraffin 
and applying it to the opposite edges of the block to be cut. Often 
the mere warming of the opposite edges of the block with a hot needle 
is sufficient. 
Another method, suggested by Dr. Land to facilitate the cutting 
of difficult material, has been tested in this laboratory and has been 
found to be very effective. Paraffin absorbs a small amount of water, 
or water penetrates between the crystals of paraffin. At any rate, 
water reaches cell walls and, perhaps, other structures which have 
not been completely infiltrated, and thus softens them. The paraffin 
cakes may be left for weeks in water. Cakes of class material may 
be put in water in a fruit can and kept until ready for use. After 
such treatment, smooth ribbons may be cut from material which 
would hardly cut at all without it. 
A ribbon carrier is very convenient. A good carrier can be made 
by mounting a couple of spools 15 or 20 inches apart, with a strong 
piece of cloth for a band. More elaborate carriers may be made if 
one has tools. 
FIXING SECTIONS TO THE SLIDE 
Mayer’s Fixative.—Sections must be firmly fixed to the slide, 
or they will be washed off during the processes involved in staining. 
Mayer’s albumen fixative is excellent for this purpose. Formula: 
White of egg (active principle). 50 c.c. 
Glycerin (to keep it from drying up). 50 c.c. 
Salicylate of soda (antiseptic, to keep out bac¬ 
teria, etc.) . 1 g. 
