To examine the electrical excitability a special battery-operated generator with constant-current rectangular impulses of 30 mA, 10 ms duration and a frequency of 50 per second is needed.
It is commercially available:

          Juergen Peschke
           Bebelstraße 49
        39116 Magdeburg
               Germany
Fax:   +49-(0)3222-1505336
eMail: j-peschke@t-online.de

Significant parameters:
constant-current rectangular impulses of 30 mA, 10 ms duration and a frequency of 50 per second