Did the original experimenter give any details as to why polarity mattered?
I do not remember he gave any.
IMO the first rabbit died due to magnitude of the applied D.C voltage and the second rabbit died, despite withstanding the current from the DC source,due to
change in polarity i.e due to a
change in DC voltage wave form.A clue to this phenomenon is provided in the paper
'A review of hazards associated with exposure to low voltages' by Dr. Marom Bikson
Department of Biomedical Engineering, City College of New York of the City University of New York,in the para
'Tissue heating depends on the RMS values of the current and little or not-at-all on its
waveform/frequency (e.g. the RMS value of a sinusoid is independent of frequency). However, for electric stimulation (shocks) the waveform of the current can have a profound influence on current efficacy (Bikson et al. 2004). AC (e.g. 60 Hz sinusoidal) is considered more likely to induce hazardous electric shocks than dc current (Camps et al. 1976; Reilly 1998). Dalziel and Lee (1969) found 10-400 Hz currents most effective in inducing involuntary hand muscle contraction. DiMaio and DiMaio (2001) considered 39-150 Hz the most lethal. Kugelberg (1976) found frequencies between 12-60 Hz most effective in inducing fibrillation of the human heart. The two competing factors relating to stimulation frequency efficacy are: 1) as electrical excitation occurs during the rising or falling phase of the current flow, increasing frequency increase the amount of potential excitations per time (e.g.involuntary muscle contractions); 2) excitable cell membranes act as low-pass filters (Bikson et al.2004), higher frequencies are thus less effective. Unless otherwise stated the results reviewed here refer to 50/60 Hz sinusoidal waveforms (as are used in power distribution systems)'