The selective action of gentian violet in relation to chemotherapy

Abstract

It is clear from the facts stated in the four previous communications that selective bacteriostasis is a complex process. The method of divided plates presents a perfect machinery for studying the workings of this process; and in the selective property of gentian violet we have a means of observing the various elements of the process under perfect control on a single plate. On such a plate we will find that

(a) Thick suspension of the Gram positive B. subtilis will not grow in the presence of the dye.

(b) By repeated re-inoculations of this organism a moderate growth can be procured on the gentian violet agar.

(c) Thick suspension of the Gram negative B. coli grow equally well on the two halves of the plate.

(d) If very weak dilutions of suspension of the Gram negative B. coli be stroked across a divided plate a few colonies appear on the plain agar, none at all on the gentian violet agar.

(e) From a suspension of the Gram negative B. coli, a gentian negative and a gentian positive strain can be cultivated.

(f) A thick suspension of the gentian negative strain of B. coli will grow equally well on the plain agar and on the gentian violet agar; if a weak dilution of the suspension be used a few colonies will appear on the plain agar, none at all on the gentian violet agar.

(g) If a thick suspension of the gentian positive strain of B. coli be stroked across the plate no growth whatever occurs on the gentian agar.

These observations indicate a number of the pitfalls which beset those who attempt to transfer laboratory observations into therapeutics. No conclusion as to the probable effect of a selective therapeutic agent is justified unless the experiments on which this conclusion is based have taken into consideration the quantities of bacteria used.