Diatoms 



FLUID WHOLEMOUNTS IN NONAQUEOUS MEDIA 



41 



all traces of grit and dried in a dust-free 

 place. As many prepared slides as are re- 

 quired now have a small drop of bromo- 

 iiaphthalene placed in each cell. If petro- 

 latum was used to hold the coverslip in 

 place while the diatoms were mounted on 

 it, this should first be removed with ether 

 to make quite certain that the diatom 

 frustules are grease-free, dry, and clean. 

 When one is satisfied as to this, the cover- 

 slip is lowered in place on top of the 

 bromonaphthalene and then, with some 

 blunt instrument (Bellido recommends a 

 toothpick) pressed on the cell until it is 

 firmly attached. If the coversUp is flat and 

 if the cell has been properly ground, this 



seal is sufficiently good to permit one to 

 remove any exuded bromonaphthalene 

 with a cloth before turning on an addi- 

 tional layer of the shellac as a final seal. 

 It is usually safer to follow this with an- 

 other layer of some impermeable cement 

 such as asphalt varnish. 



Though this process may sound labori- 

 ous, it actually takes less time by this 

 means to mount one each of the 200-300 

 species that may be found in a fossil de- 

 posit on a single coverslip than it takes 

 either to mount them individually on 

 separate sHdes by any other means, or to 

 endeavor to find them under a microscope 

 if they are arranged at random. 



