DC electric fields - Paramecia

[Martin Parnham]

Hi folks
The Ludloff phenomenon was named after the late Victorian scientist who was one of the first to observe the characteristic change in the motion of lo cilia in response to an applied electric field. In many organisms this results in a sudden change in direction.
In order to look at this I created an experimental slide using sticky back copper tape and voltage supply leads. The copper tape is 50um thick, with the glue a total thickness of about 70 um. It is widely available on the net and sold as slug repellent tape! I used the 6mm wide tape, 2 strips with an 18mm gap between them. This allows for a 2mm overlap with the cover slip at each side. I soldered 2 crocodile clips with leads along the bottom edge of the electrodes, the transient heat should not damage the glass.

Finished slide with leads.jpg (41.81 KiB) Viewed 1126 times

I made a simple wooden connection block using a couple of nails. This helps take the weight of the leads and off the slide and soldered joints, the power leads can then be clipped onto the nails.
The power supply could be a battery, I used a variable DC supply. I then used a centre off double pole double throw switch (DPDT) to make a polarity reversal 'circuit'. I mounted this on a simple construction of offcuts hot melt glued together. The centre position is 0V the top and bottom positions reverse the polarity output.

Connection block with DPDT.jpg (111.15 KiB) Viewed 1126 times

I included a multimeter in series with the output configured as an ammeter to check that the cell is conducting and working. Electrolysis may produce gas bubbles, and the copper may need cleaning occasionally - a gentle rub with alcohol.

Final assembly.jpg (154.49 KiB) Viewed 1126 times

The video records some of my observations with Paramecia. I used 3% Methyl Cellulose to slow them down and give me a chance to track them. Similar sizes drops of sample and Cellulose were mixed on the slide with a mounted needle prior to adding the cover slip. The trick is to create just enough total volume so that contact is made with the copper electrodes, but not so much the it becomes difficult to focus. Practise and patience is needed!
For more detailed observation I used a little oat 'milk' in addition to the Cellulose (not very scientific measurement - I dipped the needle into the milk to pick up a couple of small drops -that seemed to work) also mixed in before the cover slip was added. This acts so that you can see the fluid flow around the Paramecium. I usually use whole cows milk but that tends to coagulate under the influence of the field, oat 'milk' less so. The cilia are difficult to see directly so the next best thing is to visualise the flow they create.
I have included a fuller explanation of the observations on the video.

The response to electric fields almost certainly has no significance to real word situations! It is an interesting side effect of the ion based mechanisms which control ciliary action and helps provide some insights into them.



Observations made with a Brunel microscope sp300, x10 / x20 objectives, achromatic, plan, oblique rheinberg, Canon EOS M50 mark II with direct projection.