Biological tissue is ver diificult to characterize. Not only is it dependent on the cleanliness of the skin, but also on the amount of sweat in the contact are, but also on the salinity of the sweat that depends on our body. In addition, between a battery also form between the electrodes and skin, and after a couple of seconds (or minutes) iontophoresis will start taking place due to the skin-electrode batter effect, thereby changing things. As soon as you go to AC excitation of the skin, things become even more complicated, as now you have different electrical characteristics for each layer of the skin, not even talking about fat. Add to that, your body also generates its own electrical signals (muscle contractions), and that your body acts as a huge antenna picking up any external electrical field, like mains.
Sure, if you use very low datarates, you might get a signal through from your finger to your toe, but that is about it.