By Alan Hodgkin and Andrew Huxley, printed as A. L. Hodgkin and A. F. Huxley. Published in Nature 144, 710–711, 21 October 1939.
Publisher record: www.nature.com/articles/144710a0
Cited passage: abstract, intracellular recording in Loligo forbesi giant axons. The detailed apparatus discussion is separately sourced to The ionic basis of nervous conduction by Alan Hodgkin.