SEXUAL CYCLE OF MALARIAL PARASITE 285 



Rosenau, by injecting intravenously filtered blood, taken from a patient at the 

 time of sporulation of the parasites caused a malarial paroxysm. No parasites 

 developed later. Another man who received a small amount of unfiltered blood 

 showed a slight paroxysm and four days later showed parasites in his blood. Hence 

 the parasite will not pass through the pores of a Berkefeld filter. 



The cycle goes on by geometric progression from the first introduc- 

 tion of the sporozoite, but it is usually about two weeks before a 

 sufficient number of merocytes rupture simultaneously to produce 

 sufficient toxin for symptoms (period of incubation). This cycle is 

 termed schizogony. It is considered that there must be several 

 hundred parasites per cubic millimeter sporulating to be capable of 

 producing symptoms. ^ 



Gametes. After a varying tfme, whether by reason of necessity for renewal of 

 vigor of the parasite by a respite from sporulation, or whether from a standpoint of 

 survival of the species, sexual forms (gametes) develop. Some think that sporozoites 

 of sexual and nonsexual character are injected at the same time. It is usually con- 

 sidered, however, that sexual forms develop from preexisting nonsexual parasites. 

 The developing gametes are often termed sporonts. Strictly, the sexual parasites 

 in the blood should be called gametocytes. The gametes take about twice as long to 

 reach maturity as schizonts. The life of a crescent has been estimated as about ten 

 days and that of the gametes of benign tertian and quartan about one-half this period. 



The gametes show two types: the one which contains more pigment, has less 

 chromatin, and stains more deeply blue is the female a macrogametocyte; the other 

 with more chromatin, less pigment, and staining grayish green or light blue is the 

 ma le a microgametocyte. When the gametes are taken into the stomach of the 

 Anophelinse, the male cell throws off spermatozoa-like projections, which have an 

 active lashing movement and break off from the now useless cell carrier and are 

 thereafter termed microgametes. These fertilize the macrogametes and this body 

 now becomes a zygote. (Following nuclear reduction with formation of polar bodies 

 the macrogametocyte becomes a macrogamete.) This process of exflagellation can 

 be observed in a wet preparation under the microscope. There is first seen a very 

 active movement of the pigment of the male gamete and finally long delicate bulbous 

 tipped flagellum-like processes are thrown off (exflagellated) and push aside the red 

 cells by their progressive motion. McCallum saw a female Halteridium fertilized 

 by the microgamete, after which it was capable of a worm-like motion (vermiculus or 

 ookinete). 



By a boring-like movement the vermiculus stage of the zygote goes through tt 

 walls of the mosquito's stomach, stopping just under the delicate outer layer of the 

 stomach or mid-gut. In three or four days after fertilization the zygote becomes 

 encapsulated and is then often called an oocyst. It continues to enlarge until at 

 about the end of one week it has grown to be about SOM in diameter and has be- 

 come packed with hundreds of delicate falciform bodies. Some only contain 

 a few hundred, others several thousand. 



Zygotes.-- In some of his observations Darling has noted that the zygote of benign 

 tertian malaria grows larger and more rapidly than that of sestivo-autumnal and that 



