Page:Popular Science Monthly Volume 50.djvu/657

Rh bodies in the absence of methods for obtaining each species separately, in pure cultures.

Thayer and Hewetson, in their admirable monograph on the Malarial Fevers of Baltimore (1895), in which they give an account of six hundred and sixteen cases observed by themselves, have summarized their observations relating to the parasite as follows:

"We have distinguished three varieties of the malarial parasite:

"1. The tertian parasite. "2. The quartan parasite. "3. The æstivo-autumnal parasite.

"(1) The tertian parasite requires about forty-eight hours to accomplish its complete development, and is associated with relatively regular tertian paroxysms, lasting on an average between ten and twelve hours, associated, almost always, with the three classical stages—chill, fever, and sweating. Frequently, infection with two groups of tertian organisms gives rise to quotidian paroxysms; rarely, infection by multiple groups of organisms gives rise to more irregular, subcontinuous fevers.

"(2) The quartan parasite is an organism requiring about seventy-two hours for its complete development. It is rare in this climate, and is associated with a fever showing regular quartan paroxysms, similar in nature to those associated with the tertian organism. Infection by two groups of the parasite causes a double quartan fever (paroxysms on two days, intermission on the third). Infection with three groups of the parasite is associated with daily paroxysms.

"(3) The æstivo-autumnal parasite passes through a cycle of development, the exact length of which has not as yet been determined; it probably varies greatly, from twenty-four hours or under to forty-eight hours or more. But few stages of development of the parasite are found, ordinarily, in the peripheral circulation, the main seat of infection being, apparently, in the spleen, bone marrow, and other internal organs. Infection with this organism is associated with fevers varying greatly in their manifestations. There may be quotidian or tertian intermittent fever, or, more commonly, more or less continuous fever with irregular remissions. The individual paroxysms last, on an average, about twenty hours. The irregularities in temperature depend, probably, upon variations in the length of the cycle of development of the parasite, or upon infection with multiple groups of organisms.

"We have not been able to separate two distinct varieties of the æstivo-autumnal parasite, though we feel that more investigation is needed upon the subject.