Igis ] 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 glass is slowly withdrawn from the alcohol so that a minimum film 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 



