Permeability of the cell

Abstract

Protoplasm is known to be permeable to some substances and not to others. The microinjection method appears to be the only method of determining whether this semi-permeability is a property of the entire mass of protoplasm or of its surface film only.

Kite 1 injected cells by the Barber pipette method 2 and claimed to have proved that semi-permeability is a property of all portions of protoplasm. His conclusions are open to criticism owing to the extreme difficulty of the method and to his having overlooked the extraordinary ability of protoplasm to form surface films over cut surfaces. The results which I 3 obtained are directly opposed to Kite's conclusions. Recently I have devised 4 a micro injection apparatus with which one can, with remarkable ease and accuracy, inject living cells by means of pipettes with a bore less than one micron in diameter.

A half molecular ammonium chloride solution in sea water is acid to neutral red. Starfish eggs stained with neutral red and immersed in this acid solution turn yellow, owing to the penetration of only the alkaline group of the dissociated salt. If, however, stained eggs be placed in an alkaline sodium bicarbonate solution, they give evidence of the penetration of only the carbonic acid group. These findings are being reported by Jacobs in the Journal of General Physiology. They confirm the observations of previous investigators that weak acids and bases freely penetrate living cells whereas strong acids and bases do not.

My experiments, described in a forthcoming number of the Journal of General Physiology, consisted in the injection of NH₄C1 and NaHCO₃ into starfish eggs stained with neutral red. In the case where NH₄Cl was used the injected area immediately changed to a red color and then underwent cytolysis.