The rickettsias of typhus are obligate intracellular parasites that multiply only in the interior of host cells. In 1937 Zinsser and his associates1 of Harvard Medical School showed that the rate of intracellular multiplication of rickettsias in Maitland tissue cultures is determined by the metabolic rate of the host cells. Under conditions of high metabolic activity, as determined by the rate of acid formation or of oxygen consumption, little or no multiplication of the intracellular parasites takes place. Only under conditions of reduced metabolic activity was active multiplication noted. This observation finds partial confirmation in the subsequent demonstration2 that riboflavin deficiency, which slows down metabolism by interfering with internal respiration, reduces the normal resistance of rats to rickettsia infection.
In order to find substances with the opposite effect, Greiff and his associates3 of St. Louis University School of Medicine have recently studied the influence of various vitamins,