Two New World strains (South Carolina and Panama) of Plasmodium falciparum had been shown by the authors [this Bulletin, 1952, v. 49, 480; 1954, v. 51, 762] to be exceptionally long-lived in the human host, surviving for a maximum of 480 and 503 days, respectively. The infections were tested for infectivity to mosquitoes (Anopheles quadrimaculatus and A. albimanus). In general, the number of mosquitoes which became infected was directly proportional to the number of gametocytes; as a rule the Panama strain gave rise to more oôcysts than the South Carolina. Early in the disease the gametocytes, though numerous, were non-infective; this period lasted usually from 2 to 4 days. The next 30 days were the most productive, infection rates in the mosquitoes reaching 98 per cent. ; then infectivity of patients with the South Carolina strain declined more rapidly than the Panama. Late in the disease, even though gametocytes might be very scanty (less than 10 per cmm.), mosquitoes still became infected, but particularly after the recurrent appearance of gametocytes. The last batch became infected on the South Carolina strain on day 321, and on the Panama on day 410.

It is pointed out that the presence in a population of people with asymptomatic intermittent parasitaemia may be highly dangerous because such cases are often undetectable in mass surveys. P. C. C. Garnham.