PICRO-NIGROSIN 
91 
absolute alcohol to clove oil and then to balsam. The general nuclear 
phenomena of propagula-formation may be followed without section- 
ing. In unfertilized Fucus eggs the nucleus stands out sharply, sur- 
rounded by radiating cytoplasmic strands. In fertilized eggs, since 
the brown color is taken out, one can follow the enlargement of the 
nucleus and its elongation, the appearance of the centrosomes and the 
spindle figure, and the reorganization of the daughter nuclei. The 
actual fusion of the egg and sperm nucleus is difficult to observe. In 
the two weeks old embryo, the structure of the multicellular body 
resulting from the division of the fertilized egg shows well; in the 
rapidly growing rhizoidal tips, the spindle figures are nicely differen- 
tiated. In Nitella the nucleus and nucleolus in the ripe oosphere are 
clearly visible through the spiral corticating cells. The latter, as well 
as the young cells and growing tips, show practically no shiinkage. 
In all cases diatoms are cleaied so that the nucleus and general struc- 
ture may be studied with ease. 
Further work is being carried on with fungi and with other mateiial 
which indicates that the combination killing, fixing and staining solu- 
tion may have a much wider range of usefulness. The experiments 
so far conducted apparently establish the following points of special 
advantage : — 
There is an unusually wide range in the time of treatment,^ — three 
hours to three days; but, even in the long period, there is little danger 
of overstaining or overfixing. 
Since excess stain and acid are removed in most cases by rinsing in 
water or in the process of running through the alcohols no special 
washing is required. 
The stain is quite insoluble in strong alcohol; therefore material 
may be kept for a long time in the higher alcohols. 
It is an exceptionally transparent stain which differentiates the 
nuclear structure in cells with dense cytoplasm. 
The fixation is usually good and if sufficient care is taken in sub- 
sequent treatment excellent permanent mounts can be made. 
The stain keeps well in Venetian turpentine or balsam. 
These facts suggest that the method, which is unusually simple, 
may be valuable in preparing material for class work and in preliminary 
cytological work on material in toto, as well as convenient for demon- 
strating cell structures which would be completely obscured by such a 
stain as Heidenhain's iron alum hematoxylin. 
