42 MORPHOLOGY OF THE BACTERIA. 
were resolved into beads with the third and fourth eye-pieces. In like 
manner the fine striae in Surirella gemma were instantly shown to be 
beaded, with perfect and brilliant definition, with the second eye-piece. 
Navicula rhomboides and an extremely delicate specimen of Pleurosigma 
attenuatum which had resisted everything below a 4th immersion, showed 
beaded strie perfectly. We were therefore encouraged to try again to 
discover flagella in the termo. Some of our specimens, nourished in 
Cohn’s nutritive fluid, were placed in a drop of distilled water, and put 
upon the supplementary stage on an ordinary slide covered with the 
thinnest cover. The utmost delicacy and tact in manipulation of the 
light is the great desideratum ; but, with this, enough may be secured to 
work with the fourth eye-piece. The light may be made to enter the 
objective at almost every angle, but it is always projected in a direction 
at right angles to the stage; and the first thing we observed when the 
objects were sufficiently slow in their movements, and at right angles to 
the light, was that the ends of the termo, which we (and all other observers, 
as far as we know) had taken for round, proved themselves to be conical, 
terminating in a sharp point. The usual appearance of B. termo, as seen 
- with a magnification of about 600 diameters, is seen in Fig.2; whilst the 
same seen with a magnifying power of 3,700 diameters (4;th and second 
eve-piece) is seen in /%g. 5, where a globular granule is seen in the end 
of each half. But with the method above referred to, the best condi- 
tions being secured, the two ends of the bacterium were distinctly pointed, 
as seen ata b, Fig. 8, and after nearly five hours of incessant endeavor 
a flagellum was distinctly seen at one end of each of two termos which 
were moving slowly across the field. The discovery was not sudden and 
transient, but lasted for at least twenty minutes. The exquisitely delicate 
flagellum was lashing rapidly the whole time; and one of its frequent 
conditions is shown in Fig. 4, the arrow indicating the direction of the 
light: but if the termo turned round at right angles, as in Fvg. 5, all trace 
of the flagellum was gone, showing that its discovery depended entirely, 
all things being equal, upon its position in regard to the light. 
“ But this observation was made only by one of us, the other not being 
present; and in pursuance of our plan we determined to see it again, 
convincing ourselves separately, and then together. After many hours 
of labor, this was accomplished ; and Fig. 6 shows one of two instances 
which we both saw together at the same time and in the same instru- 
ment. It was lying still, obliquely across the field, the light coming in 
the direction of the arrow. Both ends were not perfectly in focus at the 
same time, but in focusing the end marked 2 6 (F%g. 6) the flagellum 
was distinctly seen, and was seen also to coil and lash; but no flagellum 
was then seen at the end c of the same object; but by bringing it into 
delicate focus it presented the aspect seen at 1 a (F%g. 6), which really 
represents the same object at the same time, only with the other end in 
the focus, while the end marked d corresponding to 2 b of Fig. 6 was in 
its turn slightly out of focus, and the flagellum lost to view. This ob- 
servation, made together, was as satisfactory as could be desired; and it 
