THE MALARIA-GERM. I97 



by the human parasite, while species of the genus Culex were selected 

 by the malaria parasites of birds. The full history, finally, has been 

 worked out in complete detail during the last two years, by Ross again, 

 and by Grassi, in Italy, and both observers reached quite independent, 

 but identical, results. Briefly summarizing these results, the full life 

 history of Plasmodium malarice may be given as follows: 



The early form of the parasite, which corresponds with the sporo- 

 zoites of the gregarine and of Coccidium, penetrates a red blood 

 corpuscle, grows to adult size, and then forms spores (Fig. 3, a — &). 

 These correspond exactly with the merozoites of the Coccidia, and, like 

 them, lead to auto-infection. At this point there is a gap in the 

 evidence, for it is not known how long this asexual method of increase 

 may continue; as shown above in the case of Coccidium, the spore- 

 forming period continues for five or six days, when a period of con- 

 jugation supervenes. It may be stated here, parenthetically, that in 

 all Protozoa, so far as known, a period of conjugation is necessary at 

 some time during the life cycle, and Avithout such conjugation, the 

 organisms, which are reproduced asexually, finally decrease in size and 

 show other signs of degeneration, ultimately resulting in death of the 

 race (see results of Biitschli, Maupas, Hertwig, etc., upon degener- 

 ating Protozoa). 



This is of considerable moment in the question of malaria, for, if 

 the malaria-organism conforms to other Protozoa, there must come 

 a time when this asexual sporulation will cease in any given set of 

 individuals, and a period of conjugation must supei^vene to give 

 renewed vigor to the parasites. So far as known at the present time, 

 this conjugation takes place only in the digestive tract of the mos- 

 quito. That it does actually take place, is undeniable from the 

 observations of MaeCallum, Ross, Grassi and others, and the con- 

 jugants again as in Coccidium, are: a small, motile, microgamete, or 

 inale cell (one of the '^flagella' of the Polymitus form); and a larger 

 macrogamete, or female, cell (Fig. 3, p — v). Their union, observed by 

 Ross and Grassi, takes place in the stomach of Anopheles, and the 

 copula then makes its way into, and through, the epithelial cells lining 

 the stomach, and finally rests against the tissue which lines the body 

 cavity. Here it grows to a relatively large size (Fig. 3, w — zz), and, 

 when mature, its nucleus divides as in the gregarine or in Coccidium, to 

 form a number of spores. Each of these develops a number of 

 germs, or sporozoites, but, unlike the sporozoites of the previously 

 described Sporozoa, these germs have no protective capsule about them, 

 and, when the parent cyst ultimately bursts, they are liberated directly 

 into the body cavity of the mosquito (Fig. 3, A, B). Here, in the 

 fluids of the body cavity, they are carried to all parts of the organ- 

 ism, and finally reach the anterior region of the thorax, where the 



