Nervous messages are invariably associated with an electrical change known as the action potential. This potential is generally believed to arise at a membrane which is situated between the axoplasm and the external medium. If this theory is correct, it should be possible to record the action potential between an electrode inside a nerve fibre and the conducting fluid outside it. Most nerve fibres are too small for this to be tested directly, but we have recently succeeded in inserting micro-electrodes into the giant axons of squids (Loligo forbesi).
Co-author with Andrew Aelding Huxley, British physiologist, (1917- ).

One of the many useful properties of giant nerve fibres is that samples of protoplasm or axoplasm as it is usually called can be obtained by squeezing out the contents from a cut end ... As in many other cells there is a high concentration of potassium ions and relatively low concentration of sodium and chloride ions. This is the reverse of the situation in the animals' blood or in sea water, where sodium and chloride are the dominant ions and potassium is relatively dilute.

The zoologist is delighted by the differences between animals, whereas the physiologist would like all animals to work in fundamentally the same way.