By means of micro-dissection and injection Amœba proteus was treated with the chlorides of Na, K, Ca, and Mg alone, in combination, and with variations of pH.

I. The Plasmalemma.

1. NaCl weakens and disrupts the surface membrane of the ameba. Tearing the membrane accelerates the disruption which spreads rapidly from the site of the tear. KCl has no disruptive effect on the membrane but renders it adhesive.

2. MgCl2 and CaCl2 have no appreciable effect on the integrity of the surface membrane of the ameba when applied on the outside. No spread of disruption occurs when the membrane is torn in these salts. When these salts are introduced into the ameba they render the pellicle of the involved region rigid.

II. The Internal Protoplasm.

3. Injected water either diffuses through the protoplasm or becomes localized in a hyaline blister. Large amounts when rapidly injected produce a "rushing effect".

4. HCl at pH 1.8 solidifies the internal protoplasm and at pH 2.2 causes solidification only after several successive injections. The effect of the subsequent injections may be due to the neutralization of the cell-buffers by the first injection.

5. NaCl and KCl increase the fluidity of the internal protoplasm and induce quiescence.

6. CaCl2 and MgCl2 to a lesser extent solidify the internal protoplasm. With CaCl2 the solidification tends to be localized. With MgCl2 it tends to spread. The injection of CaCl2 accelerates movement in the regions not solidified whereas the injection of MgCl2 induces quiescence.

III. Pinching-Off Reaction.

7. A hyaline blister produced by the injection of water may be pinched off. The pinched-off blister is a liquid sphere surrounded by a pellicle.

8. Pinching off always takes place with injections of HCl when the injected region is solidified.

9. The injection of CaCl2 usually results in the pinching off of the portion solidified. The rate of pinching off varies with the concentration of the salt. The injection of MgCl2 does not cause pinching off.

IV. Reparability of Torn Surfaces.

10. The repair of a torn surface takes place readily in distilled water. In the different salt solutions, reparability varies specifically with each salt, with the concentration of the salt, and with the extent of the tear. In NaCl and in KCl repair occurs less readily than in water. In MgCl2 repair takes place with great difficulty. In CaCl2 a proper estimate of the process of repair is complicated by the pinching-off phenomenon. However, CaCl2 is the only salt found to increase the mobility of the plasmalemma, and this presumably enhances its reparability.

11. The repair of the surface is probably a function of the internal protoplasm and depends upon an interaction of the protoplasm with the surrounding medium.

V. Permeability.

12. NaCl and KCl readily penetrate the ameba from the exterior. CaCl2 and MgCl2 do not.

13. All four salts when injected into an ameba readily diffuse through the internal protoplasm. In the case of CaCl2 the diffusion may be arrested by the pinching-off process.

VI. Toxicity.

14. NaCl and KCl are more toxic to the exterior of the cell than to the interior, and the reverse is true for CaCl2 and MgCl2.

15. The relative non-toxicity of injected NaCl to the interior of the ameba is not necessarily due to its diffusion outward from the cell.

16. HCl is much more toxic to the exterior of a cell than to the interior; at pH 5.5 it is toxic to the surface whereas at pH 2.5 it is not toxic to the interior. NaOH to pH 9.8 is not toxic either to the surface or to the interior.

VII. Antagonism.

17. The toxic effects of NaCl and of KCl on the exterior of the cell can be antagonized by CaCl2 and this antagonism occurs at the surface. Although the lethal effect of NaCl is thus antagonized, NaCl still penetrates but at a slower rate than if the ameba were immersed in a solution of this salt alone.

18. NaCl and HCl are mutually antagonistic in the interior of the ameba. No antagonism between the salts and HCl was found on the exterior of the ameba. No antagonism between the salts and NaOH was found on the interior or exterior of the ameba.

19. The pinching-off phenomenon can be antagonized by NaCl or by KCl, and the rate of the retardation of the pinching-off process varies with the concentration of the antagonizing salt.

20. The prevention of repair of a torn membrane by toxic solutions of NaCl or KCl can be antagonized by CaCl2.

These experiments show directly the marked difference between the interior and the exterior of the cell in their behavior toward the chlorides of Na, K, Ca, and Mg.

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