APPENDIX A 255 



Gold-Size is to be obtained from dealers in microscopic 

 requisites : it is used for sealing up slides, and a layer of it may 

 with advantage be applied after sealing with asphalte, or 

 Brunswick black. 



Gum Arabic is occasionally used as an embedding medium 

 for very small objects. 



Hsematoxyiin. A number of preparations of this colouring- 

 matter are in use ; of these the following are those generally 

 employed for vegetable tissues : 



1. Alum Solution of Hsematoxylin. Dissolve 0^35 gramme of 

 haematoxylin in 10 c.c. of water, and add to it a few drops of a 

 solution of alum consisting of I gramme of alum to 10 c.c. of 

 water. 



2. Kleinenberg's Haematoxylin. Saturate some 70 per cent, 

 alcohol with calcium chloride ; let the mixture stand for twelve 

 to twenty-four hours over alum, shaking occasionally ; add 8 

 parts of 70 per cent, alcohol ; filter, and then add a solution of 

 haematoxylin in absolute alcohol until the liquid has a purple-blue 

 colour ; let it stand in a corked bottle exposed to sunlight for 

 about a month ; it is then fit for use. The liquid is to be diluted 

 as required with alum solution. This preparation is most 

 generally employed, and it may be bought from the dealers 

 ready for use. 



3. Expose a few crystals of haematoxylin to the action of 

 gaseous ammonia in a watch-glass under a bell-jar : then add 

 water, and a good colouring fluid is obtained. The disadvantage 

 of this is that it has to be freshly prepared every time it is 

 required. 



The alum solutions will stain all parts of the cell, including 

 the cell-wall. Their special uses are (a) to make the cell-walls 

 more evident when they are naturally transparent and colour- 

 less ; (b} to stain the protoplasm, so as to make its intimate 

 structure apparent ; (c) to stain the nucleus, so as to demonstrate 

 its presence and to show up its structure. 



The ammoniacal solution is especially adapted for differenti- 

 ated staining. If a dilute solution be used, the first thing to 

 become stained is the chromatin of the nucleus, then, after a 

 time, the rest of the nucleus (achromatin), then the protoplasm. 



