Starting from a general equation which deals with the population balance of particulate and discrete particles in a flow reactor, the interdivisional growth of bacterium, Azotobacter vinelandii has been assessed from experimentation on this size distribution of the cells and relevant calculation. Interrelationships between the specific growth rate based on cell number and cell volume, and another relation between the generation time with and without the concept of interdivisional growth have been discussed. The fact that the bacterial growth and division are in sharp contrast with the physical phenomena such as liquid-liquid dispersion and crystallization which are superficially similar to this topic has been emphasized.