Injection of certain cellular constituents of mycobacteria into mice simultaneously with, or shortly after, infection with Staph. aureus or with Myco. fortuitum, markedly shortened the life of the infected animals. This infection-enhancing effect could be achieved by injecting the cellular constituents by either the intravenous, the intraperitoneal, or the subcutaneous route.

Suspensions of killed mycobacteria were injected into mice which had been infected several months before with small doses of various bacterial pathogens and which still harbored small numbers of living organisms in their organs. Under these conditions, a marked increase in the numbers of living bacteria in the organs of the treated mice could be detected within a very few days after treatment with the mycobacterial products, and a certain percentage of the animals died rapidly.

One of the first and most constant manifestations of the change in the infectious process from the chronic to the acute state was the appearance of a large microbial population in the liver. This happened even though Staph. aureus and Myco. fortuitum are rapidly cleared from the liver of normal mice.

In addition to killed cells of BCG and of Myco. fortuitum, pertussis vaccine and the purified lipopolysaccharide (endotoxin) of Gram-negative bacilli also proved capable of converting chronic bacterial infections into acute infectious processes.

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