The different in the substance spectrum of incubated plaque produced by the change from glucose to sucrose is insignificant. 2. A variation in the buffer capacity, such as is typical for cariogenic plaque in vivo, markedly influences the proportional composition of the acids formed. 3. The product spectrum of a mixed bacteria population such as in plaque is time dependent. The reason for this dependence is probably the interaction of the individual types of bacteria with each other. 4. The spectrum of acid composition extracted from the plaque is different from that in the vicinity of the plaque.