EUGLENAS
The Euglena gracilis are unicellular micro-organisms about 50 micrometers in length which can swim at a speed of about 100 micrometer/second. Below are some movies which show their movements.

(1) FILMS SHOWING EUGLENAS IN MOVEMENT

(a) In 2 dimensions (low magnification)

Film eug4a.mov. Euglenas between slide and slip cover (2-dimensional motion, duration=77s)
Film eug4a.mp4. Same film as above but in mp4 format
Film eug4a.gif. Same film as above but in gif format
The conclusion that it is a 2-dimensional system can be confirmed by the fact that two euglenas never really cross one another at right angle. Sometimes the ends of their bodies can be seen to overlap but the entire bodies never cover one another.
Advice If none of the 3 previous formats can be opened by your computer (notice that a right click may enable you to select the appropriate sofware), you can convert the film into other formats on the following website:
http://video.online-convert.com/

(b) In 2 dimensions (high magnification)

Film eug10a.mov. Euglenas between slide and slip cover
Film eug10a.mp4. Euglenas between slide and slip cover
This film is similar to the previous one but with a magnification that is 2.5 times larger. Again one sees that the euglenas do not cross one another at right angle.

FILM: Same film as above (format: gif)

(c) In 3 dimensions

Film ftd.mov. Euglenas in a drop (3-dimensional motion)
Film ftd.mp4. Euglenas in a drop (3-dimensional motion)
Of course, those euglenas which, at a given moment, are not in the focal plane will appear as out of focus grey spots. The more distant they are from the focal plane, the more blurred their image will be. One sees many cases where the trajectories of two euglenas intersect but they are at different levels. The image of one of them (which is in the focal plane) is sharp while the image of the other (which is above or below) is fuzzy.

(2) EUGLENAS FORMING A CLUSTER

FILM (10Xd.mov): transition zone between a cluster and the surrounding population
FILM (10Xd.mp4): transition zone between a cluster and the surrounding population
In this experiment the euglenas were confined within a thin (the thickness was about 80 micrometers) layer of water surrounded in the x-y plane by a roll of oil and comprised in the z-direction between two thin glass plates (slide and slip cover). The purpose of the roll of oil is to prevent evaporation. Without it evaporation of the water precluded any observation longer than about 5mn.
The cluster was brought about by increasing the intensity of the light directed from above. The cluster did not appear within the disk where the intensity was highest but on a darker zone at its periphery. The experiment could be reproduced almost identically; the formation time of the cluster was always about 5mn.
This experiment was performed in the group of Prof. Michel Gho to whom we express our gratitude.

(3) VELOCITY DISTRIBUTION

The following graphs show the velocity distribution of the euglenas at 3 different densities; from left to right the density decreases: 17 euglena/sq-mm, 5.3 and 2.2.
Not surprisingly, one observes that the average velocity decreases when the density increases. More interesting is the variation of the coefficient of variation, i.e. the standard deviation divided by the mean. However, to get a clearer view additional experiments are required.
Velocity distribution of euglenas

(4) LATTICE FORMATION OF EUGLENAS
In this experiment the euglenas were confined in two connected disk-shaped areas. The depth of the water was 0.5mm. The euglenas were kept in darkness (except of course when the picture was taken). The lattices on each side appeared about 30mn after the euglenas had been introduced into the pool.

  • Lattice formation of euglenas (left-hand-side)
    Same lattice magnified

  • Lattice formation of euglenas (right-hand-side)
    Same lattice but in complementary colors and magnified