848 The American Naturalist. [September, 
in plasmolyzed bacteria have often been mistaken for spores. In weak 
salt solutions the phenomena of plasmolysis disappears in an hour or 
two; in strong solutions it disappears much sooner. This disappear- 
ance of plasmolysis and the reappearance of motility bear no relation 
to each other, but depend upon entirely different causes. To obtain 
good plasmolyzed cover-glass preparations that will fix and stain in 
that condition, the author recommends putting a trace of bacteria into 
a drop of a weak salt solution (0.25 to 0.50 per cent NaCl or 0.5 to 
1.0 per cent KNO,) and then carefully spreading out the drop so that 
it will dry in 3 to 10 minutes. The bacterial cell consists of a mem- 
brane, a protoplast in the form of a wall covering, and of cell sap, and 
has, consequently, the same structure as any other plant cell. Cell nu- 
clei are still to be sought; a “centralkérper” is never present, when 
there seems to be one it is a misinterpretation due to the contracted 
protoplast, as in case of Biitschli’s observations on Spirillum undula. 
In weak salt solutions which cause distinct plasmolysis (2.5 per cent 
KNO,; 1.25 per cent NaCl, ete.) motile bacteria continue to move, 
often for hours. In stronger solutions (5-10 per cent KNO, etc.), the 
movement ceases in a few minutes owing to the benumbing of the fla- 
gella, which, however, are never drawn back into the body of the ba- 
cillus, being in this respect quite like the motile organs of the Flagel- 
lata and unlike pseudopodia. In salt solutions which do not inhibit 
growth, but are strong enough to produce rigidity of the flagella, these 
organs continue to be produced. The same is true when 0.1 per cent 
carbolic acid or picric acid is added. Motility reappears when these 
inhibitory substances are removed. As in the flagella of the Flagellata 
the cilia of the Infusoria, and the lashes of ciliated epithelium the 
movement of the flagella in the bacteria is not independent of the 
protoplast, but nevertheless continues when the latter is disturbed by 
plasmolysis. Apparently, as in case of crushed infusoria a small frag- 
ment of the protoplast remaining attached to the base of the flagellum 
is sufficient to continue the movement. Rigidity of the flagella can be 
brought about in various ways—lack of oxygen, acid reactions, too 
much salt, mal nutrition, or the addition of poisons. On removal of 
these injurious influences the motility returns. In case on non-motile 
cultures of the hay bacillus the addition of ł per cent asparagin suf- 
ficed to induce motility quickly. In the making of cover-glass prepa- 
rations various changes may take place in the flagella, they may be 
thrown off, or inrolled, or become swollen so as to be unstainable and 
unrecognizable. The inrolled flagella never unroll. They often ap- 
pear as little foamy heaps of rings around the bacteria (typhoid bacil- 
