Anopheles sinensis from Shanghai and Guangxi were experimentally infected with Ha-inan and Guangxi strains of Plasmodium vivax. It was found that both anopheline mos-quitoes had a very low susceptibility to the Guangxi strain, the gland infection rate being 0 and 12.3% (43.2% for Are, minimus serving as control), while they showed distinctly higher susceptibility to the Hainan strain, the respective gland infection rate being 36.4% and 43.6% (100% for An. minimus).Two lots of An. sinensis from Wuhan were experimentally infected with Guangxi strain of P. vivax from two patients. It was shown that they had just the same low susceptibility as An. sinensis from Guangxi. The gland infection rate of the two lots of mosquitoes was 4.6% and 30.6% respectively, although it has already been confirmed that An. sinensis from Wuhan was highly susceptible to the indigenous strain of P vivax. From the present experimental results and literature, it is evident that there exist in China different geographic strains of P. vivax with varied infectivity to Are. sinensis.

39 healthy volunteers were experimentally inoculated with Plasmodium vivax from Guangxi by mosquito bite, and 32 of them were successfully infected. 25 of the infected volunteers (78.1%) had a short incubation period (mean: 16.4 days) prior to the onset of malaria attack, while seven individuals had long-term incubation period of 238 to 314 days (mean: 274.7?29.3 days). Relapses occurred in all cases with short-term incubation period after a long latency without exception; most of them had l to 2 relapses, some, 3 relapses. Among the seven cases with long incubation period, only one relapse occurred in five, and the remaining two had no relapse at all. It was shown that although Guangxi was situated in subtropical zone, Plasmodium vivax there was characteristie of the temperate zone type. A comparison of Plasmodium vivax from Guangxi with those from south Yunnan and Henan suggested that they differ in the composition of sporozoite subpopulations classified arbitrarily according to the duration of development of bradysporozoites in hepatic cells.