1915] LAND—MICROTECHNICAL METHODS 401 
Softening refractory material imbedded in paraffin 
Plant material, especially if much starch is present, will not cut 
readily in paraffin. For complete infiltration with paraffin dehy- 
dration must be thorough, and a corresponding hardening of tissues 
results. 
As is well known, paraffin is pervious to water. If imbedded 
material impossible to cut without fragmentation or tearing of the 
sections be stored in water for some weeks or months it will in most 
instances section readily. The effect of water on imbedded material 
will be most strikingly shown if an attempt is made to cut the game- 
tophyte of some of the cycads at or just after fertilization of the egg 
immediately after imbedding, and again after the paraffin cakes 
have lain for some months in water. Dormant embryos of Helian- 
thus which will not ribbon immediately after imbedding give 
unbroken ribbons after the paraffin block has been soaked for some 
weeks in water. The writer stores in water all paraffin containing 
hard material. 
A method of cleaning cover glass 
In attempting to clean cover glasses 50-60 mm. long by wiping 
with a cloth after they have been freed from the cleaning fluid, 
many are broken even with the most skilful and practiced handling. 
Also it is almost impossible to have them free from lint. 
In the writer’s practice cover glasses are placed in the usual 
cleaning fluid used for laboratory glassware, a mixture of sulphuric 
acid and potassium bichromate, rinsed under a tap to completely 
remove the acid, placed while wet in alcohol, and finally completely 
submerged in 95 per cent alcohol until wanted. To use, the cover 
glass is slowly withdrawn from the alcohol so that a minimum film 
of alcohol will remain on the glass, one end touched to a piece of 
absorbent paper free from dust to remove the drop of alcohol, 
touched to a flame, and when the alcohol has completely burned off 
placed while warm on the slide. 
This method is very rapid and gives beautifully clean cover 
glasses with practically no breakage. If the cover glass is drawn 
from the alcohol so slowly that a very thin film remains, a small 
crack in the cover glass will not spread. 
University oF CHICAGO 
