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 

 aifrnuatum which had resisted everything below a ^th 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 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 (^th 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 condi- 

 tions being secured, the two ends of the bacterium were distinctly pointed, 

 en at a 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 

 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 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 b (Fig. 0) the flagellum 

 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 (Fig. G), 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 



