1. The investigation of different physiological properties of dextral and of sinistral forms of Bacillus mycoides shows that in the basic features of their metabolism these strains coincide with one another. Both in sinistral and in dextral strains the natural dextrorotatory arginine proves to be more suitable material for growth than the racemic arginine. Both the sinistral and the dextral strains oxidize the natural dextrorotatory glucose equally well and with the same temperature coefficient.2. The specific difference between the dextral and the sinistral strains is not consequently connected with the inversion of the basic protoplasmic system, but with differences in some secondary substances determining the cellular form. On the basis of the study of the phenomenon of heat injury in the growth of morphologically inverse dextrally twisted strains of Bacillus mycoides the hypothesis is advanced that some organic substance, participating in the determination of the cellular form, has undergone an optica...