26 BACTERIA IN RELATION TO PLANT DISEASES. 
the contrary, as much.as possible should be made out of morphology, particularly 
that of the living organism, and in this connection the recent efforts of Migula and 
Fischer are especially deserving of commendation. 
MOTILITY. 
If motile, determine kind of motion and rapidity 
(margin of small hanging drops on thin covers sus- 
pended over hollow-ground slides).+ The cover may 
be prevented from sliding by touching one edge with 
a very little vaseline or cedar oil; if too much is 
used it runs under, mixes with the hanging drop, and 
spoils the mount, and possibly in the end the objec- 
tive is ruined, if the student continues to search for a 
clear field. The beginner is very apt to mistake 
Brownian movement for self-motility. It sometimes 
requires very careful observation to be quite certain. 
Rods which appear to be motionless will sometimes 
be seen to dart away quite suddenly if watched. In 
some species young cultures are much more apt to 
be motile than old ones ; in others motility appears 
to be an almost constant characteristic. The move- 
ments of bacteria are sometimes quite characteristic 
for particular sorts. ‘They may be slow or rapid 
tumbling motions centering in the shorter axis, or 
straight or sinuous slow or rapid darting move- 
ments in the direction of the longer axis, with 
rotation on this axis. ‘The media of Hiss (’97, Bib- 
liog., XVI) and of Stoddart (’97, Bibliog., XVI) are 
sometimes useful for distinguishing macroscopically 
between motile and non-motile forms. ‘The former 
spread as a thin layer over the whole surface, the 
latter pile up in restricted areas around the points 
of inoculation. ‘The student should not remain con- 
tent with merely determining motility, but when this 
has been settled he should turn his attention to 
staining the organs of motion. 
*Fic, 24.—Upright Zeiss camera for photomicrographic work. The cup (a) slips over the end 
of the microscope and forms a light-tight connection with the bellows without touching it. The 
microscope rests on the table independent of the camera. The stout rod turns freely in the socket 
X and is locked in place’ by a set-screw on the side opposite the observer. The height is about 
45 inches. 
{Lehmann and Fried (Arch. f. Hyg., Bd. XLVI, 1903, p. 311) found the swiftest movement of 
bacteria to be 1 mm. in 22 seconds; the slowest I mm. in 222 seconds; average: cholera, 1 mm, in 
3414 seconds; typhoid, 1 mm. in 56 seconds; B. vulgare, 1 mm. in 73 seconds; B. subtilis, 1 mm. in 
4o seconds; B. megaterium, I mm, in 2 minutes Ir seconds, 
de 
