284 THE INFECTIOUS DISEASES. 



penetrate the flagella iu the form of long thin rods which remain after 

 the flagella become detached. The shell of the red cell in which the 

 crescent has developed can rarely be seen in fresh preparations of the 

 flagellate forms. These flagella penetrate the body of one of the macro- 

 gametes present in the slide and fertilize it. 



This process, which we have followed in an artificial preparation, seems 

 necessary for the continuance of the race, and is normally carried out in 

 the middle intestine of the mosquito of the genus Anopheles. The 

 actual entry of the microgamete (spermatozoon) into the macrogamete 

 has been observed by MacCallum ' and others in fresh blood prepara- 

 tions. 



If a patient in whose blood mature crescents are present is bitten by 

 the mosquito, the parasites develop in the intestine of the insect, and at 

 the end of two days the fertilized forms may be found adherent to the 

 wall of the intestine as small pigmented oval bodies quite similar to the 

 early forms of the crescents developing in the human bone marrow. Two 

 days later, the parasites or oocysts are much larger and have a distinct 

 capsule, while by the sixth day they may measure from 60 to 80 // in diam- 

 eter. They contain numerous small particles which are nuclei due to 

 the frequent division of the original nuclear material, and the capsule is 

 much thicker. At the end of a week the parasite contains a large num- 

 ber of slender thread-like rods with pointed extremities, each one of these 

 rods having nuclear chromatin. The parasite or oocyst projects through 

 the wall of the intestine into the coeloni cavity of the mosquito host, 

 and when it ruptures these minute rods or sporozoites are carried by the 

 lymph currents to the salivary glands from which they may be injected 

 with the saliva when the female Anopheles bites another subject. 



The sporozoites, after entering the circulation of man, attack the 

 red cells, and become the small amreboid forms described above. In 

 two to three weeks the formation of the gametes takes place, and the 

 crescent forms appear in the blood. 



That the infection of man in this way is possible has been abundantly 

 proven by allowing mosquitoes infected with sestivo-autumual organisms 

 to bite healthy persons, who, after a period of Incubation of about ten 

 days, are seized with an sestivo-autumual type of fever, and the character- 

 istic organisms, though not present previously, are now to be found in 

 the blood. The mature forms or gametes of the tertian and quartan fevers 

 undergo a course of development very similar to that of the sestivo-autum- 

 nal fever, and are derived from the blood of the infected patient by the 

 female of the same genus of mosquito, the Anopheles (Plate I., Figs. 19 

 and 30). The sporozoites find their way to the salivary glands of the 

 mosquito and enter the blood of the person infected while the Anopheles 

 is biting. These sporozoites then enter the red cells as the small amoe- 

 boid forms and carry on the sexual cycle in the blood until either the 



1 MacCallum, "On the Haematozoan Infections of Birds/' Jour, of Exp. Med., vol. 

 iii., 1898, p. 117. 



