PERMANENT PREPARATIONS. 113 



The sections stained with safranin, methyl- violet carmine, or 

 fuchsin-logwood, can be enclosed in glycerine- jelly. Chemically 

 pure glycerine is also an excellent medium in which to enclose 

 these preparations, but needs the edges of the cover-glass pro- 

 perly sealed. This can be done with a solution as thick as treacle 

 of Canada balsam in chloroform, benzol, xylol or turpentine, 1 or 

 gold-size may be used if the cover-glass edge is quite clean, for 

 gold-size does not cling to a surface damped with glycerine. 

 After laying on the cover-glass, any glycerine which flows out 

 should be carefully removed with blotting-paper, and the closing 

 medium laid in a streak round and over the edge of the cover- 

 glass by means of a thin glass rod which has been dipped into 

 it. This should be laid on in only a thin layer, and should not 

 much overlap the cover- glass. To enable a preparation mounted 

 in or closed with Canada balsam to be subsequently examined 

 with a homogeneous immersion lens it is desirable to cover the 

 edge, after it is quite dry, with a thin layer of gold-size, for which 

 purpose a fine camel-hair brush is most suitable. The gold- 

 size should be laid on very thin, and a second layer if necessary. 

 Gold -size is not affected by the immersion oil, while Canada 

 balsam is. Finally it is well to exercise judgment in the use of 

 all mounting fluids, carefully proportioning the size of the quan- 

 tity taken to the size of the cover-glass used and the apparent 

 thickness of the section, i.e., to the space which the mounting 

 fluid has to fill. With practice this is by no means difficult, and 

 it is possible to put up section after section without any overflow 

 of the mounting fluid at all. If the amount necessary be slightly 

 under- estimated, a little pressure on the cover- glass may effectively 

 compensate. 



For the removal from one fluid to another of large sections, 

 the edges, of which readily fold over, we can use, though with 

 care, small section lifters of platinum, or of beaten copper wire, 

 such as are recommended in the Introduction. 



The stem of the Oat (Avena sativa), or of some other grass, 

 can be taken instead of Zea Mais, should this latter not be 

 available. In all these cases the vascular bundle will be found 



1 Of these the solution in turpentine is best, as it does not become brittle 

 when dry ; otherwise a jerk may make the cover-glass spring. The solution 

 can be kept in a bottle with a bell-shaped external ground cap, to keep out 

 the air. [ED.] 



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