TWO FIGURESWhen potassium is lost from an animal cell, sodium enters. This exchange may be brought about either by immersing the cells in a lowpotassium medium or by stimulation in a normal medium. I n most instances, the analytical work showing this exchange has been done on tissues and the results are complicated by the necessity of allowing for the tissue spaces outside of the cells themselves. This is usually done on the basis of measurements of the chloride space, although recent results by Heilbrunn and Hamilton ('42), tend to cast some doubt on the exact interpretation of results obtained by the usual analytical methods. The giant axons of the squid offer a material from which adequate amounts of pure axoplasm can be collected uncontaminated by extracellular material. Bear and Schmitt, ('39), and Webb and Young ('40) have analyzed axoplasm, and reported results. The latter authors did not use pure axoplasm, however, but analyzed whole nerves and calculated the axoplasm space. The results reported in this paper were obtained during a series of experiments designed to show the exchange of sodium and potassium in axoplasm collected as free from contamination as possible.

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PHYSIOLOGY: H. B. STEINBACH tween the Vo and the proton should be the same as between the neutron and the proton, at least as far as both potentials are due to the interaction with 7r mesons. Under this assumption, the scattering cross-section for the collision of Vo particles with protons or neutrons is very nearly equal to the proton-neutron scattering cross-section at the same energy. If it should be possible to measure the former cross-sections it would give a clue concerning the validity of the analogy between heavy particle conservation and charge conservation laws.

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