160 METHODS OF MICROSCOPICAL EESEARCH. 



and the cover is to be laid upon a slip, with the 

 balsam upwards, and held over the flame of a 

 Bunsen burner until the balsam is liquefied; the 

 polycystina are then to be evenly spread upon the 

 cover by means of a needle ; when the balsam is 

 cold a small drop of benzol-balsam is to be placed 

 upon its surface and a clean half -inch cover to be 

 warmed and carefully lowered upon the balsam. 

 The polycystina will thus be mounted between two 

 covers; now turn the "mount" over, so that the 

 under surface of the lower cover shall be upwards, 

 and coat this with asphalt, put the mount aside for 

 a day or two, in order to allow the asphalt to be- 

 come thoroughly hard, then having made in the 

 centre of a slip a disc of asphalt of the same 

 diameter as the "mount," and allowed that also to 

 dry thoroughly, put upon this disc a small drop of 

 (cold) " French liquid glue," 1 place upon this the 

 asphalted under surface of the " mount," and when 

 the glue is quite dry finish off the slide with either 

 asphalt or white zinc cement. 



1 This is to be obtained from any chemist, and is a most 

 admirable, reliable, and cleanly cement. 



