Microscopy. 277 
upon glass. Lampblack will not, in its ordinary form, mix with 
plaster. A variety of colors may be obtained by using the ‘ Flor- 
entine Fresco Colors’ sold by F. W. Devoe & Co., New York. 
They may be mixed with the plaster. The chrome orange, chrome 
yellow, Venetian red and ivory black have been on trial in tablets 
for about a week, and show no change under the alcohol. 
“The use of plaster in tablets is not claimed to be new with the 
writer, but this method of manipulation and coloring is the result 
of independent experiment, and may therefore present some fea- 
tures of interest. Tablets as above prepared have proved, in my 
experience, superior to those made of wax in the matter of cost, in 
the facility with which they are to be prepared, and in neatness of 
appearance.” 
PREPARATION OF THE Eaes OF ASCARIS MEGALOCEPHALA.— 
Through the researches of M. Nussbaum,! Ed. van Beneden,? J. B. 
arnoy,’ and Otto Zacharias,‘ the egg of Ascaris megalocephala of 
the horse has become a classical object for the study of fecundation. 
In the simple structure and enormous size of its nuclei, this egg 
offers unequalled advantages for such study. But a very serious 
drawback is found in the thick impervious egg-membrane, which 
is capable of resisting for a long time the action of preservative 
reagents. Dilute acetic or nitric acid requires at least from eight 
to ten days to penetrate; and alcohol of 40 to 50 per cent., two or 
three months. Development goes on undisturbed in osmic acid of 
per cent.; and several days are necessary even for absolute alco- 
hol to take effect. 
For tracing the karyokinetic phenomena of fecundation, it is of 
the utmost importance to find reagents that will kill and fix quickly, 
as reliable preparations of transitory stages in nuclear metamor- 
. Phosis cannot be expected with reagents that penetrate slowly, 
o Zacharias *® has discovered an acid mixture which overcomes 
the resitence of the egg-membrane, and fixes the egg completely 
Within 25 to 30 minutes. The mixture consists of 
Alcohol (90 to 100 per cent.) 80 cem. 
Glacial acetic acid 20 cem. 
Osmic acid (1 per cent.) 20 to 30 drops. 
A little glycerine or chloroform increases the clarifying power of 
the mixture, 
a Archiv f. mik. Anat,, xxiii., 1884. 
: Archives de Biol., iv., 1884. 
: 1e top ape 1886-7, 
reniv f. mik. Anat., xxx., H.1, 1887. pe 
Pt Ueber Abtédting und Färbung der Eier von Ascaris megalocephala. 
atomischer Anzeiger, iii., 1, p. 24, Jan., 1888. i 
