By nuclear and cytoplasmic criteria we believe we have demonstrated the occurrence, in patients infected with a pure strain of P. vivax, five series of cells, which for convenience we have designated A, B, C, D and E. Of these series C and series D are the well known micro- and macro-gametocytes. The cells of series A reproduce by schizogony, and are generally recognized as trophozoites. Our observations lead us to entertain the opinion that at the schizogony of certain cells in series A, a merozoite differentiated from the others is produced (figs. 48 and 110), which gives rise to a schizont of either series B or D. The cells of these series we regard as pregametocytes. On the schizogony of the cells of the pregametocytes of series B or D, the merozoites become the gametocytes of either series C or E respectively. The cells of series A thus may be regarded as stem cells for the other series, and are numerically the backbone of the infection. Our present observations do not suggest the existence of more than one series of stem cells, from which it is likely both sexes of gametocytes are produced by the schizogony of the intermediary pregametocytes. Our inability to detect more than one series of stem cells suggests that the sporozoites which initiated the attack were not sexually differentiated.
In a paper (1) to appear shortly by Boyd, Stratman-Thomas and Muench, it is shown that frequent oscillations of gametocyte density occur, with upward trends recurring at five day intervals. If, as appears probable, the cells of series C or E require 48 hours for maturation, and the cells of series B or D are assumed to require the same period until they produce gametocytes on schizogony, a total of 96 hours are required for the production of gametocytes from the stem cells. With afternoon paroxysms the development would require a period of five days, an interval in line with observations reported in the study cited.