The view that the essential factor in the transmission of the state of excitation from region to region in an irritable protoplasmic system (such as nerve) is a form of electrolytic distance action, dependent on the formation of local electrical circuits between the active and the resting regions of the protoplasmic surface, 1 has various implications, some of which can be tested by experiment. It is to be expected, for example, that the speed of transmission will be a direct function of the electrical conductivity of the external medium, since this medium is traversed by the local current between the active and the resting regions. This current, in order to have stimulating effect at a given distance from the active region, must have a certain intensit), at that distance, corresponding to the threshold intensity of electrical stimulation under the conditions; evidently this intensity will be decreased if the electrical conductivity of the medium is lowered. According to the local action theory of transmission, the speed (V) of the activation wave is proportional to the product of this critical distance (s) into the rate (r) of the local activation process (V -st); hence any decrease of external conductivity (other conditions remaining equal) must, by decreasing s, decrease correspondingly V. A close proportionality between the conductivity of the medium and the speed of transmission has in fact been observed in the nervous network of the medusa" in various dilutions of sea water, and in vertebrate and invertebrate muscle? Since 1LiUie, R. S., Am.

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1. Exposure of unfertilized starfish eggs to dilute solutions of weak acids (fatty acids, benzoic and carbonic acids) in isotonic balanced salt solution causes complete activation with the proper durations of exposure. For each acid the rate of activation (reciprocal of optimum duration) varies with concentration and temperature; at a given temperature and within a considerable range of concentrations (e.g. 0.00075 to 0.004 M for butyric acid), this rate is approximately proportional to concentration. We may thus speak of a molecular rate of action characteristic of each acid. 2. In general the molecular rate of action increases with the dissociation constant and surface activity of the acids. In the fatty acid series (up to caproic), formic acid has the most rapid effect, acting about four times as rapidly as acetic; for the other acids the order is: acetic = propionic ≦ butyric < valeric < caproic. Carbonic acid acts qualitatively like the fatty acids, but its molecular rate of action is only about one-fourteenth that of acetic acid. 3. Hydrochloric and lactic acids are relatively ineffective as activating agents, apparently because of difficulty of penetration. Lactic acid is decidedly the more effective. The action of both acids is only slightly modified by dissolving in pure (isotonic NaCl and CaCl2) instead of in balanced salt solution. 4. The rate of action of acetic acid, in concentrations of 0.002 M to 0.004 M is increased (by 10 to 20 per cent) by adding Na-acetate (0.002 to 0.016) to the solution. The degree of acceleration is closely proportional to the estimated increase in undissociated acetic acid molecules. Activation thus appears to be an effect of the undissociated acid molecules in the external solution and not of the ions. Acetate anions and H ions acting by themselves, in concentrations much higher than those of the solutions used, have no activating effect. The indications are that the undissociated molecules penetrate rapidly, the ions slowly. Having penetrated, the molecules dissociate inside the egg, yielding the ions of the acid. 5. When the rate of activation is slow, as in 0.001 M acetic acid, the addition of Na-acetate (0,008 M to 0.016 M) has a retarding effect, referable apparently to the gradual penetration of acetate ions to the site of the activation reaction with consequent depression of dissociation. 6. An estimate of the CH of those solutions (of the different activating acids) which activate the egg at the same rate indicates that their H ion concentrations are approximately equal. On the assumptions that only the undissociated molecules penetrate readily, and that the conditions of dissociation are similar inside and outside the egg, this result indicates (especially when the differences in adsorption of the acids are considered) that the rate of activation is determined by the CH at the site of the activation reaction within the egg.