THE PERMEABILITY OF THE ARBACIA EGG TO AMMONIUM SALTS

¹ From the Department of Physiology, University of Pennsylvania, and the Marine Biological Laboratory, Woods Hole, Massachusetts

1. The rate of swelling of Arbacia eggs in solutions isosmotic with sea water of the ammonium salts of the first five saturated fatty acids has been found to be in the order: valerate>butyrate>propionate> acetate>formate.

2. In solutions of these salts made up in bicarbonate-free sea water or in M/2 KCl recovery of the original volume after a preliminary shrinkage follows the same order.

3. Within the pH range from approximately 7.8 to 6.2 the rate of swelling increases with increasing acidity. Under certain conditions a further lowering of the pH may reverse the effect.

4. No significant changes in volume occur in solutions of ammonium nitrate or chloride, though cells exposed to such solutions for over an hour are still capable of swelling in ammonium acetate.

5. These results agree with the theory suggested by Jacobs, that there is no appreciable penetration of either the salt or its ions as such but that undissociated ammonia and fatty acid, formed by hydrolysis of the salt, penetrate the cell separately, uniting again after their entrance.

6. The rate of entrance of the acid, rather than that of the ammonia, usually appears to be the limiting factor in determining the rate of swelling of the cell.