V. H. Blackman . 
182 
slight shake is given to the vessel, for, as with Noctiluca and other 
luminous organisms, Pyrocystis when floating quietly gives out no 
light at all. An attempt was made to observe them under the 
microscope by their own light in order to determine, if possible, the 
portion of the cell from which the light arose. The time during 
which they normally remain luminous, after shaking, is hardly 
: uTicient for the purpose, but by stimulating them artificially the 
period of luminosity can be much prolonged. 
By the addition of 1% acetic acid, in quantities sufficient to bring 
the fluid in which the Pyrocystis is floating up to .05%, the indi¬ 
viduals, on shaking, both shine more brightly and remain shining 
for a longer period. Quinine dissolved in acetic acid has the same 
effect, but absolute alchohol gives the most marked results. A 
few drops of this fluid added to 15 cc. of water containing P.pseudo- 
noctiluca has some stimulating action, for on shaking they shine 
out more brightly than normal specimens and remain in a lumi¬ 
nous condition longer; but the best results are obtained only by 
the use of much larger quantities. On adding very gently one-third 
of its volume of absolute alcohol to sea-water containing this form 
and various Peridineae, and mixing the fluid carefully, a few speci¬ 
mens of Pyrocystis shine out brightly, but the full effect of the 
alcohol is only produced on violent shaking, the fluid then glows as 
one mass and remains luminous for two to four minutes. A part of 
this luminosity is due to small Peridineae, but Pyrocystis can be dis- 
tinquished as large and exceptionally brilliant spots in the glowing 
mass. It is strange that such a large quantity of alcohol should be 
required, it can only be explained by the fact that fluids penetrate 
very slowly through the wall, as is shown by an experiment in 
which some specimens of this species were allowed to fall into 0.5% 
chromic acid, in this fluid they remained luminous for five to ten 
seconds. Luminous specimens of Pyrocystis which have been 
stimulated by alcohol, can be placed on a slide and observed by 
their own light under a low power of the microscope in the dark. 
On comparing later such a view with that obtained with trans¬ 
mitted light, it appears that the radiation arises from the mass of 
protoplasm surrounding the nucleus. The specimens observed 
were, however, in a contracted condition, so that it may be that in 
a normal state the protoplasm generally may be luminous, as in 
Noctiluca. John Murray (7) simply states that u Pyrocystis is 
strongly phosphorescent, the light proceeding from the nucleus,” 
but the latter statement can hardly be accepted without a consi- 
