Part VIII.
1. Cross-immunity experiments in the guinea-pig, rabbit and monkey were carried out with the viruses of the tsutsugamushi disease (including rural typhus) and the urban typhus of Malaya; they showed that immunogenically the two viruses are distinct.
2. The characteristics of setiology, epidemiology, serology and experimental infections are compared, and the conclusion drawn that the two diseases belong to entirely separate groups of rickettsial disease.
Part IX.
1. Cross-immunity experiments in the guinea-pig and rabbit were carried out with the viruses of Rocky Mountain spotted fever, tsutsugamushi (including rural typhus) and urban typhus. They showed that, immunologically, tsutsugamushi
and spotted fever are entirely distinct; whereas urban typhus and spotted fever, though more distinct than alike immunologically, do possess a minor degree of reciprocal cross-immunity.
2. Spotted-fever vaccine was found to have no protective value against the viruses of tsutsugamushi and urban typhus.