Abstract
It is well known that malignant tumors produce a greater amount of lactic acid than the large majority of normal tissues. It appeared to us, therefore, of interest to study the effect of lactic acid on the proliferative activity of different kinds of cells and organisms. We undertook experiments on the influence of lactic acid on the growth of paramecia, yeast, rats, and malignant tumors. We neutralized the C.P. market preparation of lactic acid with sodium hydroxide until the different pH's desired were obtained. Lactic acid solutions were prepared varying between pH 3 and pH 7. In each experiment distilled water acidified with so much hydrochloric acid that the same pH was obtained as in the lactic acid solution was used as control. In our experiments with paramecia we found that pure lactic acid is very toxic because of its strong hydrogen ion concentration. In a solution of lactic acid 1:5,000 the paramecia died within a few minutes, and even when the solution was weakened to 1:10,000 a high mortality of the paramecia was noted. Lactic acid in the concentration of 1:1,000 neutralized with sodium hydroxide to pH 7 kills the paramecia within one or 2 days. Weaker solutions of lactic acid such as 1:5,000 at pH 7 begin to inhibit the multiplication of paramecia after some time, and kill these organisms after from 5 to 7 days. This can be seen in the following table. This table shows one of our many experiments in which we compared the rate of multiplication in paramecia in hay extract alone (control) and in the same kind of hay extract after the addition of lactic acid in a concentration of 1:5,000. In each experiment we used 8 watch glasses, 4 of which served as controls, and 4 of which contained lactic acid.
Published Version
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