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1894.] Microscopy. 977 
<“ Vorfarben ") such as affect the cytoplasm and the nucleus, and 
leave the centrosomes unstained. Thus the chemical affinities of the 
centrosomes for the hematoxylin would remain at full strength, while 
those of the cytoplasm and nucleus would be more or less saturated, 
and to the same extent weakened for the hematoxylin. In this way 
the process of extraction was brought under some control, and the 
method greatly improved. 
Stains reached in this way are called “subtractive.” 
Bordeau R., Anilin blue and Methyl-eosin were employed as pre- 
liminary stains. Bordeaux R. proved to be the best. In preparations 
that have been successfully differentiated as to the centrosomes, the 
nucleus and its chromatin are almost colorless, so that the centrosome 
may be easily studied, even when it lies behind the nucleus. The nu- 
€leoli remain strongly stained. F 
The Chromatin—Heidenhain shows that there are two kinds of 
chromatin to be distinguished, namely: an oxychromatin brought out 
by acid anilin stains (e. g., Rubin S.), and a basichromatin which is 
brought out by basic anilin stains (e. g., Methyl green). The “ basi- 
chromatin " is the chromatin of Flemming and authors in general. 
The differentiation of the two chromatins can only be accomplished 
when the nucleus is exposed at the same time to both acid and basic 
anilin colors, asis the case when Biondi's solution and Ehrlich's triacid 
are used. 
If one mixes ammonium vanadate with hematoxylinum pur (Grübler) 
a blue stain is obtained which stains cytoplasm and oxychromatin 
strongly, while the basichromatin is often left nearly colorless. 
The two chromatins probably differ only in the amount of phosphorus 
present, basichromatin containing more, oxychromatin less. 
The Egg-Centrosome.'—Dr. H. Mertens finds that the so-called 
“ yolk-nuclei," so generally known in both vertebrate and invertebrate 
eggs, represent, in the case of the mammals and birds, two very differ- 
ent elements. Sometimes they are chromatin granules eliminated 
from the nucleus; at other times they represent centrosomes. The 
identification of these bodies with the centrosome is the point of chief 
interest. The method employed was as follows: The material was 
prepared in Hermann’s fluid. Three precautions were observed: (1) 
The object must remain a long time in the fluid—for weeks or even 
months. (2) Transfer to pyroligneous acid (1-3 ds.). (3) Wash 
thoroughly in running water. foes 
The preparations were imbedded in celloidin and stained with safra- 
nine, 
*H. Mertens, Arch. de Biologie, XI, 3, '94, p. 394. 
