TECHNIQUE. 47 



hollowed out in a block of hard paraffin. The osmic 

 acid solution is placed within this cell, the latter being 

 filled to within a short distance of the surface. The 

 edge of the paraffin cell is then smeared with vaseline 

 and the cover glass then placed preparation-side 

 downward over the cell, and pressed into the vaseline, 

 thus making an air-tight junction. After exposure to 

 the vapor for from 30 seconds to 1 minute the prepa- 

 ration is at once placed in absolute alcohol, and after- 

 ward stained, and mounted in acid-free Canada bal- 

 sam. At no stage of the process should the specimen 

 be allowed to dry if the best cytological results are 

 desired. The osmic acid mixture preferred consists of 

 20 parts of a 4 per cent, osmic acid solution and 1 part 

 of glacial acetic acid. 



Various staining methods may be used in coloring 

 the parasitic amoeba3 of man. Among the most simple 

 are carbol-fuchsin, methylene blue, gentian violet and 

 hsematoxylin. The latter is most valuable in demon- 

 strating these parasites and Delafield's haematoxylin 

 gives the best results. It should be well diluted with 

 distilled water and the preparations should be left 

 in it over night, after which they are washed in run- 

 ning water, and, if well stained, are rinsed in 50 per 

 cent., 70 per cent., 90 per cent., and absolute alcohol, 

 and mounted in Canada balsam, which is free from 

 acid. If the specimens are too deeply stained they 



