298 
NOTES AND MEMORANDA. 
rection without having recourse to very different materials, as e. g. 
strong acetic acid. (4) On the other hand, a proper time must be 
allowed for the necessary operation of washing, so that the colour 
does not disajDpear if the washing is prolonged somewhat. The aniline 
colours hitherto employed do not permit this. (5) The preparations 
must be capable of being viewed and preserved in a medium of small 
refractive power. This is not possible in the case of haematoxylin 
staining, and where aniline colours are used. (6) The stain must be 
a fixed colour. All these conditions are satisfied in the pigment which 
is called Bismarck brown. The application of it is very simple. A 
concentrated solution of it in water or weak alcohol is used. To 
obtain the former quickly, the pigment must be boiled in distilled 
water, which serves at the same time to prevent the formation of the 
white film to which it is subject. The solution is then filtered (the 
filtration requires to be repeated from time to time). Sections of 
alcohol or chromic acid preparations are stained immediately on 
being put into such a solution, which is of a dark brown colour ; if 
the solution is weaker, but still strong, the sections become deeply 
stained in a few minutes. The differentiation of the staining is effected 
in a few minutes by washing in absolute alcohol, and then the pre- 
parations (cleared by oil of cloves, &c.), may either be kept in Canada 
balsam, or put up direct in glycerine. In the latter case, care must 
be pa’d to the washing in alcohol, and it is as well to put the pre- 
paration previously in distilled water again. No harm at all is 
done if the section is left a day or two in the staining fluid, or allowed 
to lie for hours in alcohol or days in oil of cloves, provided the stain 
is not too weak in the first instance. 
The nuclei are stained brown by it, and, as with all good stains, 
more or less dark according to their size. Many protoplasms and 
connective tissues stain a more or less light yellow. Amyloid is 
not plainly differentiated, but plasma-cells and many bacterian forms 
are, which resist hiematoxylin and carmine stains. Double staining, 
&c., can be applied, of course, as well as with other pigments for 
nucleus staining. From an aesthetic point of view, the colour will 
not perhaps give satisfaction. This, however, is a matter of taste, 
and the tint has the advantage that preparations thus stained can be 
photographed. Our blue and red stains are badly adapted for photo- 
graphing. 
Thin Covering Glass . — A complaint is made in the ‘ Zeitsch. f. 
Mikroskopie ’ that the covering glass supplied from England in 
recent years is of bad quality, not only being of excessive thickness, 
but containing bubbles and a number of microscopic points which 
cannot be removed by any chemical means, so that a great part is 
unsuitable for any delicate investigations. Complaints addressed 
to the manufacturers have, it is said, met with no success. 
Improved Form of Frog-plate . — With the common brass frog-plate 
generally used it is almost impossible, after the frog has been properly 
secured, to move the plate under the clips which in the cheaper 
microscopes serve to retain the object in place on the stage. A very 
