The penetration of arsenic into living cells 1

Abstract

The purpose of these experiments was to study directly the penetration of arsenic into living cells. The organism used was the fresh water alga Nitella, which furnishes single cells several inches in length, whose contents may be easily expressed and analysed. Freshly collected cells only were used.

To determine whether there is any relation between H ion concentration and arsenic penetration ten .033 M phosphate buffer solutions were made up covering the range P_H 5.6 to 7.5, and at least twenty-five cells of Nitella placed in each of these for each experiment. After 24 hours counts were made of the number of cells still in good condition, i.e., turgid and with cell sap clear and free from chloroplasts.

A series of similar experiments was performed in which arsenic in the form of atoxyl was added to the buffer solutions in sufficient quantity to make the concentration of atoxyl .05 M; and still another series in which a set of 0.05 M arsenate buffers was used (arsenic acid plus NaOH) having the same P_H range as the phosphate buffers. In each case the proportion of cells of Nitella still in good condition after 24 hours in the solutions was determined.

In both experiments with arsenic the sap of all the cells in good condition was expressed (precautions for preventing contamination being taken), a constant quantity (0.036 c.c.) incinerated, and the arsenic determined by the Gutzeit method, which is sensitive to about one micromilligram.

All experiments were conducted at laboratory temperature, which was usually not far from 20° C.

1. The influence of both hydrogen ions and buffer salt ions upon the condition of Nitella is shown by the facts that:

a. In phosphate buffers of .033 M the proportion of cells surviving in good condition was greatest, (92 per cent.) at P_H 6.2, and decreased when the medium was more acid or alkaline.