CHAPTER XX. 



CEMENTS AND VAENISHES. 



458. Introduction. — Two, or at most three, of the media 

 given below will certainly be found sufficient for all useful 

 purposes. For many years I have used only one cement 

 (Bell's). I I'ecommend this both as a cement and varnish ; 

 gold size may be found useful for turning cells ; and Mii.lek's 

 caoutchouc cement may be kept for occasions on which the 

 utmost solidity is required. Mai-ine glue is only necessary 

 for making glass cells. 



For the operations of mounting in fluids, and of making- 

 cells and ringing, see O.^epentee's The Microscope. 



Caepentek lays great stress on the principle that the 

 cements or varnishes used for fluid mounts should always be 

 such as contain no mixture of solid particles, for those that 

 do always become porous after a certain lapse of time. All 

 fluid mounts should have the edges of the cover carefully dried 

 and be ringed icitJi glycerin jelly before applying a cement ; 

 hy this means all danger <f running in is done aivay ivith. 

 See §§ 460 and 461. But no method yet devised will make 

 a glycerine mount absolutely permanent. 



See also Atjbeet, The Microscojw, xi, 1891, 150, and Journ. 

 Roy. Mic. Soc, 1891, p. 692 ; Beck, The Microscope, xi, 1891, 

 pp. 338, 368, and Journ. Roy. Mic. Soc, 1892, p. 293; 

 Beheens' Tabellen ziom Gebrauch bei miltroslcopischen Arbeiten 

 (Bruhn, Braunschweig, 1892) ; Eodsselet, Journ. Quek. Mic. 

 Club, vii, 1898, p. 93 ; and as to the comparative tenacity of 

 divers cements, Beheens, Zeit iviss. Mil\, ii, 1885, p. 54, and 

 AuBEBT Amer. Mon. Mic. Journ., 1885, p. 227; Journ. Boy. 

 Mic. Soc, 1886, p. 173. — Beheens gives the palm to amber 

 varnish ; Aubeut places Millee's caoutchouc cement at the 

 head of the list, Lovett's cement coming lialfway down, and 



