The influence of a number of fluorescein derivatives on the growth of yeast in sunlight and in the dark was studied, in a manner similar to that described in the preceding communication. A 0.5 per cent or 1 per cent suspension of yeast in 5 per cent or 10 per cent of cane sugar was generally employed and the quantity of CO2 evolved was measured. To such suspensions of yeast in sugar solutions, the following fluorescent compounds were added in concentrations varying from 1:50,000 to 1:250,000. The sodium salt of fluorescein itself; the potassium salt of tetra-brom-fluorescein (eosira); the potassium salt of di-bromfluorescein; the sodium salt of tetra-iodo-fluorescein (erythrosin); the potassium salt of tetra-chlor-fluorescein, the chlorine being introduced into the phthalic residue; the potassium salt of a chlorinated fluorescein with the chlorine introduced into the resorcin component; and the potassium salt of sulphone fluorescein. These compounds were prepared at the request of the author by Dr. E. White through the courtesy of the research laboratories of Hynson, Westcott, and Dunning Co. It was found that in concentrations 1:100,000, none of the dyes produced any appreciable effect in yeast fermentation in the dark. In stronger concentrations (1:50,000) eosin produced a slight inhibition. When exposed to direct sunlight, in concentrations of 1:50,000 all of the dyes produced a slight inhibition of the yeast. When however, the same dyes were aidded to yeast suspensions in direct sunlight together with small quantities of sodium benzoate a remarkable synergistic effect was noted. The inhibitory power of the combinations on the fermentation power of the yeast was pttentiated two hundred and even more per cent, as compared with either dye or sodium benzoate alone. Thus solutions of eosin 1:100,000 plus sodium benzoate 1:1000, in direct sunlight produced an inhibition two or three times as great as that produced by either eosin or soaium benzoate alone.