The problem of the stability of the development of Shigella population in the intestine, depending on the dose of the infective agent, is analyzed. The agent is reproduced in the intestinal mucosa in short cycles, starting with adhesion and followed by penetration, intracellular multiplication and, finally, emission of free bacteria and hulled tops of villi with Shigella intracellular microcolonies. This form of emission maintains high concentration of bacteria and ensures, in case of the adhesion of hulled material, high local concentration provoking the repetition of the cycle. Depending on the dose, chains of cycles either progressively develop or maintain a constant level, or become extinct. Stable development of the chains of infectious cycles forms a focus of infection in the body (in the intestine). The growth of the populations of infective agents in live tissues, following the chain of cycles, produces a new type of microbial culture, differing from the types obtained by batch and flow cultivation. The aggregation and accumulation of infective agents in the hulled material is the particular case of the formation of infections, highly active particles and accumulations of infective agents, ensuring the development of infection with a relatively small number of organisms.