ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



983 



" Another stain that the histologist, and especially the student of 

 micro-botany, frequently has occasion to use, is the so-called indigo- 

 carmine, or sulph-iudigotate of jjotash solution. Like the foregoing 

 (picrocarmine) the text-books content themselves with recommend- 

 ing it, but giving no working formula for preparing it. 



The following process gives a brilliant beautiful blue that works 

 well with almost any kind of preparation, and is most useful in double 

 staining of vegetable sections. Take of the best indigo, in lump, 30 

 grains. Powder in a capsule, and dry thoroughly in a water bath. 

 When perfectly dry, add 2 drachms (by weight J of fumiug (Nord- 

 hausen) sulphuric acid, adding it drop by drop, and stirring with a 

 glass rod. As the indigo swells under this treatment, a large capsule 

 is necessary. The whole of the acid having been added, stir well, 

 cover, and let stand for twenty-four hours. Transfer to a tall flask, 

 and add 3 ounces of distilled water. Let stand for four days, giving 

 the flask an occasional shake. A magnificent blue colour is now 

 obtained, but its acidity prevents its being used in this condition. 

 The solution must now be neutralized by the addition of carbonate of 

 potash (or soda) added cautiously, with frequent testings, as an excess 

 of the alkali causes the separation of the indigo in a doughy mass 

 (which can be redissolved, however). Filter the neutralized solution, 

 and evaporate to dryness. For use, dissolve in fifty times its weight 

 of distilled water." 



Mercer's Solid Watch-glass.* — Dr. A. C.Mercer uses the "Syra- 

 cuse Solid Watch-glass " (fig. 162) as a bath, or staining or dissecting 

 dish for the histological la- 

 boratory. It rests solidly 

 upon the table or stage, and 

 is not liable to be overturned 

 and its contents spilled. 

 It is transparent and can 

 be used over black, white, 

 or coloured paper, enabling 

 the student to use such 

 backgrounds for his work 

 as will permit him to watch 

 its progress to the best 

 advantage. Transparent tissues can be examined in it from time to 

 time, or dissected and studied on the stage while in water, alcohol, 

 oil of cloves, or other bath, enabling the student to reject unsatis- 

 factory specimens at any step in the process of preparation. 



When the top and bottom edges are cut, one watch-glass rests 

 dust-tight up(m another, and a piece of plate glass will fit accurately 

 over it as a cover. In such a watch glass, covered, specimens may 

 remain for long staining or soaking, without loss of fluid by evapora- 

 tion. When the concave surfaces are polished, the watch-glass is 

 as clear as a lens, and becomes a perfect receptacle for transparent 

 dissecting material on the sta^e. 



Fig. 162. 



The Microscope, iv. (1884) pp. G7C-7. 



