THE WATER OR ALCOHOL METHOD. 211 



effect is not obtainable by means of one of these manoeuvres 

 alone. 



This simple process is very useful for the preliminary exa- 

 mination of trial sections whilst cutting. It is often suffi- 

 cient to put on a cover, warm, withdraw the melted paraffin 

 by means of a cigarette paper, and run in a drop of clearing^ 

 agent. 



In the primitive form given above, G-aule's method is use- 

 ful enough for the purpose of mounting a small series of sec- 

 tions that do not require to be stained or otherwise further 

 manipulated on the slide. Later workers have by improve- 

 ments in the details of the process brought it to a state of 

 great perfection, so that it may now be considered a fairly 

 safe process for extensive series of sections, and will allow of 

 staining on the slide. 



SUCHANNEK (Zeit. f. wiss. Mik., vii, 4, 1891, p. 464) pointed 

 out that the slides must be absolutely free from grease in order 

 that the alcohol (50 per cent.) or distilled water, which may 

 be used instead, may spread out in a thin and uniform layer. 

 Secondly, that the slides should not be warmed to more than 

 40 C., it being important both that the alcohol should evapo- 

 rate slowly and that the paraffin should only be softened , not 

 melted, until the evaporation is complete. HOYER had already 

 for this reason advised slow evaporation at the temperature of 

 the laboratory. 



GULLAND (Journ. of Anat. and PhysioL, xxvi, 1891, p. 56; 

 Journ. Roy. Mic. Soc., 1892, p. 161) floats sections on to the 

 surface of warm water (not warm enough to melt the paraffin), 

 or alcohol if preferred, in a dish, and thence floats them into 

 position on the slide. The slide is drained, and the water 

 evaporated from it at a low temperature as described above 

 (Gulland says c< a little under 50 C.," which of course is only 

 a low temperature relatively to a paraffin of what I consider 

 an undesirably high melting-point). When the water of the 

 sections has evaporated completely they become more trans- 

 parent, and look dry. The fixation is then complete, the 

 paraffin may be melted and removed by means of any desired 

 solvent, and the sections may be mounted, or be stained in 

 any medium, or otherwise manipulated as desired. Thin sec- 

 tions will generally be fixed in about an hour ; thick ones will 

 require six hours or more. Here it may be pointed out that 



