SECTION TWO 



necessary for fluorescence microscopy, but provided they are not 

 more than 1-3 mm. in thickness ordinary microscopic shdes have 

 been found quite satisfactory. 



Notes on fluorochromic staining technique: 



(a) Fixatives containing salts of heavy metals (with the exception 

 of zinc); chlorine, bromine, iodine, and nitro compounds should 

 be avoided as these exert a quenching effect on fluorescence. The 

 most suitable fixatives are 5 to 10% formalin, or Kahle's fluid. 



(b) If tissues are embedded in paraffin wax, all traces of the wax, 

 which is auto-fluorescent, must be removed before sections are 

 stained and examined. 



(c) A special grade of immersion oil known as fluoroil (E. 

 Gurr, 195 1 ), which is non-fluorescent, should be used for high- 

 power examination, since cedarwood oil and most of the immer- 

 sion oils available for ordinary microscopy are unsuitable for 

 fluorescence work. 



(d) The usual mounting media, as used for ordinary micro- 

 scopy, contain highly fluorescent materials which render them un- 

 suitable for fluorescence work, and should, therefore, be avoided. 

 For temporary mounts, glycerine may be used, and for permanent 

 mounts there is a satisfactory xylol miscible medium on the 

 market under the name of Fluormoimt (E. Gurr, 195 16). However, 

 if the fluorochrome used is removed from the tissues by alcohols, 

 dehydration has to be avoided, in which case permanent prepara- 

 tions can be made by mounting direct from water in Uvak which 

 is a moderately quick-drying, aqueous, non-fluorescent mountant. 

 The coverslips can be secured firmly immediately after mounting 

 by the application of Laktoseal. 



Fluorochromes, of which auramine O, coriphosphine, acridine 

 yellow Hi 07, aesculine, acridine orange, primuline, thiazole yellow 

 are examples, are frequently used in very dilute solutions to pro- 

 duce characteristic fluorescent colours, and when preparations 

 which have been treated with these solutions are examined in trans- 

 mitted light of the visible spectrum, they appear to be unstained 

 or only very faintly tinted. 



Some explanation as to the colour differentiation obtained by the 

 use of general-purpose fluorochrome of which acridine yellow 

 Hi 07 is an example, is offered by the fact that fluorescence 



103 



