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Journal of Experimental Biology 17,353-363 (1940)
Published by Company of Biologists 1940

Studies on the Physiology of Arenicola Marina L. : II. Accommodation to Magnesium Concentration in the Isolated Extrovert

G. P. WELLS ¹ and ISABEL C. LEDINGHAM ¹

¹ Department of Zoology, University College, London

1. The reactions of the isolated extrovert of Arenicola marina to variations in the external Mg concentration are described and discussed.

2. Artificial sea water supports a vigorous rhythm for many hours and was therefore arbitrarily taken as the "normal" saline. In all mixtures, the following were held constant: pH, K, Ca, sulphate, osmotic pressure. Increase in Mg was osmotically compensated by decrease in Na, and vice versa.

3. High Mg concentrations depress, and low ones raise, the spontaneous activity level of the preparation.

4. The preparation can accommodate itself, to a large extent, to a new Mg concentration. The effects of abruptly changing to a new mixture are greatest just after the change, and gradually become less as accommodation occurs.

5. After accommodation to a new Mg concentration, the old is no longer appropriate. Return to artificial sea water evokes Mg-deficiency reactions after accommodation to high Mg, and Mg-excess reactions after accommodation to low Mg. In either case, the preparation slowly accommodates itself back again to normal.

6. The accommodation process occurs in mixtures whose Mg concentration is so high that spontaneous activity cannot reappear. This is shown by the fact that Mg-deficiency reactions are evoked by changing back to normal after long exposure to such mixtures, and proves that accommodation does not depend on special events (such as permeability changes) associated with functional activity.

7. If time enough for accommodation is allowed, or if the change of Mg concentration is made very slowly ("drift" experiments), it is found that fairly normal activity can occur over a wide rage--from Mg-free mixtures to mixtures containing about three times the amount of Mg in sea water. At the upper end of this range, the preparations are, however, markedly depressed.