Measurements of ion concentrations and of electrical potential difference and resistance have been made in Artemia salina, the brine shrimp, using animals acclimatized to sea water. It is believed that the results of the electrical measurements are largely determined by the characteristics of the gill epithelium. The potential difference between the blood and external medium in sea water is + 23 mV. (blood positive). Considered in relation to the ionic concentrations, this indicates that

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... e is subject to active transport out of the animal, potassium is pumped in, and sodium is approximately in equilibrium. Measurements of potential difference in other solutions give the permeability ratios Na:K:Li:Cl as 1·00:0·6: 1·0:0·11. The resistance of the gill epithelium in sea water is 40 Ωcm.2. Measurements of resistance in other solutions suggest that lithium ions induce a decrease in cation permeability.