Complex sentence: At the time Murdoch started testing his gun the only tranquilliser drugs available were curare, and alkaloids of nicotine, both of which tended to have fatal reactions in a high percentage of animals shot.
Split into simpler sentences: At the time Murdoch started testing his gun the only tranquilliser drugs available were Curare and alkaloids of nicotine. Both of which tended to have fatal reactions in a high percentage of animals shot.