KARYOKINESIS AND ITS RELATION TO FERTILIZATION. 189 
sideration is given to the nucleoplasm, which yet forms so 
important a constituent of the nucleus. 
When Sattler (177) and myself studied in 1882 the Frog’s 
skin for nuclear division by employment of lunar caustic 
we always obtained only nuclear figures of Remak’s earlier 
scheme, never karyokinetic figures, whereas we were easily able 
to demonstrate the latter in Frog’s skin otherwise treated. 
We sought in vain to obtain chromatic figures in the divi- 
sion by means of silver. We obtained nothing. We ex- 
pressed ourselves, indeed, in the following terms (p. 275) :— 
“Tf one tries to explain the differences of structure as 
shown by silver method and nuclear stains, the only admissible 
supposition appears to be that the other appearance of silver- 
nuclei must be due to the achromatic substance of Flemming, 
which Iwould now call ‘nuclear sap.’ Thisdoes not become evi- 
dent by means of nuclear stains ; at least it is masked in contrast 
to the striking pattern which is presented by the chromatic con- 
stituents of the nucleus during division. Silver always brings 
out the structure of the complete nucleus with its chro- 
matic and achromatic substances, and one sees by the appear- 
ances obtained that the achromatic substance exhibits an ame- 
boid movement during division, but in other respects during 
division behaves itself according to the simpler division- 
scheme. One must therefore deduce from the effect of stains 
and silver that the more fluid achromatic nuclear substance 
always remains around the nuclear fibres, and is not diffused 
in the cell-protoplasm, but shares in the nuclear network ; 
whilst, therefore, the chromatin of the nucleus successively 
passes through the well-known striking changes in position 
and form, the achromatic substance divides in a simpler way, 
since it always forms a sort of envelope for the chromatic 
figure.” 
Recently Pfitzner (157), in his very remarkable work, has 
produced real proofs of this, so that it may be regarded as a 
fact. He succeeded in rendering visible during division 
simultaneously the chromatic thread figure and the rest of the 
constituents of the nucleus, which he now includes, with the 
