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Experiments

sea-water, water, distilled, acid and cent

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EXPERIMENTS.

Studies of recent years have shown the important influence of hydroxyl and hydrogen ions upon the rate of nerve-conduction. The free hydroxyl ion is a stimulant through a considerable range of con centration, but the free hydrogen ion is a depressant, excepting that in very weak concentration it acts as a moderate stimulant. Thus, if sea-water be diluted with acid distilled water of about P„ 5.5 (H-ion concentration 0.316 X the rate of nerve-conduction is augmented in slight dilutions, but it declines more and more rapidly in dilutions of 80 per cent sea-water plus 20 per cent distilled water and over. The muscular activity, as measured by the amplitude of the pulsation wave, usually declines steadily in sea-water diluted with acid distilled water of P„ 6, while when diluted with alkaline water of P„ 8 it maintains itself or even augments.

Table 2 shows the effect upon the muscular activity as measured by the amplitude of the pulsation wave in Cassiopea when taken from natural sea-water and gradually run into diluted sea-water composed of 50 volumes sea-water plus 50 volumes distilled water (50 per cent sea-water), at 30° C.

Thus when sea-water is diluted with alkaline distilled water, more than half the rings show augmented muscular activity, whereas if the distllled water be slightly acid the muscles of more than half are depressed, and this depression is much more marked the greater the acidity of the distilled water used in diluting, so that with distilled water of about 5.5 P. the amplitude of muscular movement is hardly perceptible in 50 per cent sea-water. As the average temperature of the sea-water was about 30° C., the neutral point was about 6.86 P. and thus it appears that even very slightly acid distilled water is usually a muscular depressant, whereas alkaline distilled water is a correspondingly efficient stimulant; this is the more remarkable when we consider that the hydrogen-ion concentration of the sea-water is very slightly augmented by dilution even with its own volume of distilled water of 6 P. Thus McClendon found that such a dilution

of sea-water of 8.1 P. changed the P. of the solution to 8.09; in other words, the relative concentration of the hydrogen ions was increased only from 1 to 1.02, such is the efficiency of the buffer carbonates in preserving the normal alkalinity of the sea-water.

It will be recalled that Osterhout (1914)* finds that a slight concen tration of HC1 is at first stimulating to plants, but later (after the plasma membranes have been penetrated by the acid) it becomes depressant. It would seem that in Cassiopea a very slight relative increase of the H ion can not penetrate the cells, but acts only on the cell surfaces or membranes and in so doing becomes a stimulant; but in stronger concentration the cell membranes are penetrated and the H ion then exerts its well-known depressant effect.

The muscles are much more sensitive to changes of concentration in 11 or OH' ions than are the nerves.

The stimulating effect of a very slight increase of acidity or of alka linity upon the rate of nerve-conduction is well shown if we place the pulsating ring in natural sea-water and then add about 5 per cent of acid distilled water of P. about 5.5, for the rate suddenly augments about 5 per cent. Similarly, if we take the pulsating ring from nor mal sea-water and place it in sea-water which has been condensed by evaporation at normal temperature in the sun to about 90 per cent of its original volume, the rate augments on account of the high alkalinity of the evaporated sea-water.

Professor McClendon made up a series of acid and alkaline sea waters. He added 23 c.c. of n/10 to each 1,000 c.c. of natural sea-water and after bubbling air through the solution for 12 hours the P. was 8.26, and a film of calcium carbonate was precipitated upon the sides of the glass flask containing the solution. Similarly, he made acid sea-waters of P,, 7 by adding to each liter 24 c.c. of n/10 HC1 and then aerating for 12 hours; and a sea-water of P. 5.6 was obtained in the same manner by aerating for only half an hour.

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