METHOnS ai' STUDY. 97 



few drops of 5 over the slide, and cover with a bell glass for an 

 hour or two. 



3. Wash well in bath 4, and judge by the colour of the 

 specimens, which should be orange-yellow, not brown, or they 

 are stained too deeply. If too deeply stained leave them in 

 the acid bath until they assume the desired tint. Practice is 

 needed in judging of this. 



4. Place the slides face upward in a large vessel, holding 

 half a gallon, of any hard water. The colour of the prepara- 

 tions will gradually change to a brilliant blue — this may 

 require an hour or more — I use ordinary London water. 



It is advantageous to place the specimens in a shallow dish, 

 through which a gentle stream of water is flowing for half an 

 hour, as a trace of acid in the albumen film causes the colour 

 to fade. I use a porcelain photographer's bath, and allow the 

 water from the tap to flow in a thin stream into one corner 

 and out of another. Specimens so prepared exhibit perfectly 

 definite nuclear staining. 



If thought desirable, a second diffuse stain as neutral carmine 

 may now be poured over the slide and washed off when the pre- 

 paration is sufficiently stained. I do not think, however, that 

 such double staining serves any useful purpose, as the logwood 

 usually gives sufficient colour to differentiate all the tissues — 

 whilst the double stain often obscures details. The lime salts 

 in the water used is a powerful mordant of Haemato.xylin. I 

 formerly rendered the water bath feebly alkaline, a glass rod 

 dipped in liq. ammonije used to stir the bath is sufficient. 

 Neither soda nor potash should be used, and the advantage of 

 using ammonia is doubtful. 



5. Transfer to a bath of 50 % alcohol, and then to a bath of 

 methylated spirit. Wash the slide with a little absolute 

 alcohol — I c.c. is sufficient — allow it to drain for a moment, 

 and drop clove oil over it with a pipette, moving it as a 

 photographer does a plate he is coating with a film or with 

 varnish. 



Drain by setting the slides on end, under a glass shade, on a 

 sheet of filter-paper. If there is any cloud it may be removed 



7 



