I assumed the battery had gone flat.
Could there be a problem a floating ground?
prevent such polarisation by periodically reversing the polarity of the electrodes by either an h-bridge type device or a DPDT relay
Try connecting the top end of the 3K3 resistor to an Arduino PWM pin instead of to +5V, and connect a 1uF ceramic capacitor in series with the electrode. Connect the analog input pin to the junction of the capacitor and the resistor. Set the PWM output to 50%. Take analog readings both when the PWM output is high and when it is low (you can read the state of the PWM pin using digitalRead), and take the difference between the two readings. This way, you will be feeding AC to the electrodes, avoiding electrolysis.
When you put the electrodes on your chest, were you trying to measure a voltage generatedby your chest ? Or were you applying a voltage from the arduino to your chest and tryingto measure the conductivity or resistance of your chest ?
I remember something about potatoes being used as batteries
1)Thank you. I shall try this. It might take me a while to sort it out, and I will need to buy the ceramic resistor, but I am keen to try it.
3) Am I correct in thinking that using the usb connector to power the arduino, rather than the 9v battery, would produce an AC current across the skin? Or does the arduino somehow only provide DC current out of the 3.3v or 5v pins? If the usb connector is AC then I could at least use that to test the effectiveness, even if I will have to implement one of the proper solutions offered above for the portable battery operated operation.
Connecting yourself to something that is connected to mains ground (such as an Arduino powered from the USB port) is a bad idea