CHAPTER XXI. 



CEMENTS AND VARNISHES. 



451. 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 recommend this as a cement and varnish ; gold 

 size may be found useful for turning cells ; and MILLER'S 

 caoutchouc cement may be kept for occasions on which the 

 utmost solidity is required. 



Marine glue is necessary for making glass cells. 



CARPENTER 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 he has always 

 found that those that do, although they might stand well 

 for a few weeks or months, yet always become porous after 

 a greater lapse of time, allowing the evaporation of the 

 li(|iiid and the admission of air. All fluid mounts should be 

 ringed with glycerin jelly before applying a cement; by this 

 means all danger of running in is done away with. See 

 453 and 454. ' 



The reader who requires more information concerning 

 microscopical cements and varnishes than can be given in 

 this chapter may consult with advantage the papers of 

 AUHERT, The Microscope, 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; BEHRENS' 

 Tabellen zum Gebrauch bei mikroskopischen Arbeiten (Bruhn, 

 I5r;mnschweig, 1892); and ROUSSELET, " On some Micro- 

 Cements/' Journ. Quekett Mic. Club, vii, 1898, p. 93. 



452. Comparative Tenacity of Cements (see BEHRENS, Zeit. f. 

 iviss. Mik., ii, 1885, p. 54, and AUBERT, Amer. Mon. Mic. 



