Bacterium ter mo. By W. E. Ballinger and J. J. Drysdale. 107 
striated clearly and sharply, but the striae 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 T Vth immersion, 
showed beaded striae 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 them- 
selves to be conical, terminating in a sharp point. The usual 
appearance of B. termo, as seen with a magnification of about 600 
diams., is seen in Fig. 2 ; whilst the same seen with a magnifying 
power of 3700 diams. (sVth and second eye-piece) is seen in Fig. 3, 
where a globular granule is seen in the end of each half. But with 
the method above referred to, the best conditions being secured, the 
two ends of the bacterium were distinctly pointed, as seen at a b, 
Fig. 8, and after nearly five hours of incessant endeavour a flagel- 
lum was distinctly seen at one end of each of two termo 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 Fig. 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 labour this was accomplished ; and Fig. 6 shows one 
of two instances which we both saw together at the same time and in 
the same instrument. 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 focussing the end 
marked 2 b (Fig. 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 
i 2 
