The Paraffin Method 113 



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 ju, when, at 10 ju, 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, or better 

 still, by Land's cooling device. 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 



i 



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. 



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. 



Salycilate of soda (antiseptic, to keep out bac- 

 teria, etc.) 1 g- 



Shake well and filter. It will keep from 2 to 6 months, but, to say the 

 least, it is never better than when first made up. Of course, white 

 of egg may be used alone, since the other two ingredients are merely 

 incidental. Put a small drop of fixative on the slide, smear it evenly 



