I’ve been incredibly lucky to be invited to work on my dissertation and current projects at Matt Ratto’s Critical Making Lab. Since last week, I started bringing the slime mold growing on plates nested in a camera bag, underneath a box of electronic components — musing for a few seconds, every now and then along the way, on the reactions such a find would involve if I ever lost that bag in the subway. I started experimenting on the slime mold with much better equipment and amazing help.
The previous post introduced the idea of resistance in the slime mold. Yesterday I got to examine just how high that resistance could be if the slime mold plates were left open even for a few minutes.
The first time I observed that connection made between the two agar blobs was last Saturday. I inoculated the slime mold on the left agar blob four days before. It went on initially exploring its environment away from the blob and oat flake on the right —as the white traces on the left blob show— before perhaps voting to make a meal of it after all.
I was eager to place that newly grown organic wire into a simple circuit, and see if I could perhaps light a LED with it. I hooked the slime mold wire to a power supply, placed a green LED on a breadboard, and started cranking up the voltage knob. 2 volts: nothing. 4 volts: nothing. 10 volts: still nothing. I kept increasing the voltage until —at about 28 volts— I noticed a faint glimmer coming out of the LED:
28.7 volts! That’s quite an amount of resistance!
Something was wrong. I had read — and been warned— that the resistance of slime mold was somewhere around 3 MΩ. I thought perhaps I had left the petri dish open for too long. But how long was too long? I checked in the Advances in Physarum Machines book, and there it was, at page 27, in a chapter contributed by Martin Grube:
In closed Petri dishes, the air humidity ranges between 95–98 % (as measured by humidity sensors), which appears optimal for growth. As soon as the lid of a containment such as a Petri dish is lifted, air humidity immediately drops to values below 70%, which exposes Physarum to an immediate desiccation shock, unless the lid is closed immediately again to restore tolerable humidity as soon as possible, in the range of several minutes.
So the next step will be to find a way to use the wires while either leaving the petri dish open for as little time as possible, or closed altogether.