134 METHODS OF MICROSCOPICAL RESEARCH. 



as Cole's exposure process. It consists in placing 

 the specimen to be mounted upon a cover glass, 

 applying exactly the quantity of balsam necessary 

 to ensure the permanent preservation of the speci- 

 men, and that the balsam shall flow to, but not 

 beyond the extreme edge of the cover, and then 

 allowing the balsam to evaporate for twenty-four 

 or thirty-six hours until all the xylol, or other 

 solvent, has left it, and the balsam has set hard 

 before mounting it on the slip. The author devised 

 a set of "pigeon holes," or. rather grooves, made to 

 take 3 in. by 1 in. slips, in which the covers could be 

 placed, lying upon slips, during the time allowed 

 for evaporation. But when the small cabinets, with 

 trays, were introduced, he found these to be, prac- 

 tically, all that is needed for this purpose. This 

 process of mounting is thus effected. A supply of 

 thin glass covers of the sizes necessary for the 

 specimens to be mounted having been cleaned, and 

 the specimens, if necessary, cleared, they are placed 

 upon the covers if sections, being floated on to the 

 covers from the clearing fluid and carefully spread 

 flat upon the covers. The clearing fluid is then 

 drained off by holding the cover with its edge 

 against a sheet of blotting-paper and the covers, 

 if f in. diameter, are placed in pairs upon slips. If 

 f in. covers are used, three are placed on each slip, 

 of course with the section, or other specimen, 

 upwards. The balsam is then applied, and the slips 

 with the covers, balsam upwards, placed in a cabinet 

 with trays so that no dust can approach them, and 

 they are left for twenty-four hours to evaporate. 

 Then a very small drop of xylol balsam is placed in 

 the centre of each of the mounts in succession ; a 



