250 ENTOMOLOGY 



Two or more sets of parasites in the human blood, sporulating at 

 different times, may cause the fever to recur at intervals that are 

 apparently irregular. 



After several successive asexual generations, there are produced 

 merozoites which develop no longer into schizonts but into sexual 

 forms, or gametes. These occur in red blood corpuscles either as 

 macrogametocytes (female, 7, 8) or as microgametocytes (male, 70, 80), 

 in which forms the parasite is introduced into the stomach of a mosquito 

 which has been feeding upon the blood of a malarial patient. The 

 macrogametocyte now leaves its blood corpuscle and becomes a spherical 

 macrogamete (9); and the microgametocyte also becomes spherical 

 (90) ; but the latter puts forth a definite number (six, in L. falciparum, 

 gb) of flagella, or micro gametes, which separate off as motile male bodies, 

 capable of fertilizing the macrogametes. A microgamete penetrates a 

 macrogamete (10) and the nucleus of the one' unites with that of the 

 other. The fertilized macrogamete, or zygote, now becomes a migrating 

 cell, or ookinete (n), which penetrates almost through the wall of the 

 stomach of the mosquito (12) and then becomes a resting cell, or cyst. 

 This ob'cyst (13) grows rapidly and its contents develop, by dire ct nuclear 

 division, into sporoblasts (14, 15), which differentiate into spindle- 

 shaped sporozoites (16, 17). The sporozoites are liberated into the 

 body cavity of the mosquito, carried in the blood to the salivary glands 

 (as well as elsewhere) and thence along the hypopharynx into the 

 body of a human being, bird or other animal attacked by the 

 insect. 



The role of the mosquito as the intermediary host of malarial organ- 

 isms was discovered by Manson and Ross and confirmed by Koch, Stern- 

 berg and others. It has been found repeatedly that certain mosquitoes 

 (Anopheles) after feeding on the blood of a malarial patient can transmit 

 the disease by means of their " bites" to healthy persons. Thus, 

 Anopheles mosquitoes were fed on the blood of malarial subjects in 

 Rome and then sent to London, where a son of Dr. Manson allowed him- 

 self to be bitten by the insects. Though previously free from the 

 malarial organism, he contracted a well-marked infection as the result 

 of the inoculation. 



Furthermore, it is highly probable that malaria cannot be trans- 

 mitted to man except through the agency of the mosquito. This ap- 

 pears from the oft-cited experiment of Doctors Sambon and Low on the 

 Roman Campagna, a place notorious for malaria. There the experi- 

 menters lived during the malarial season of 1900, freely exposed to the 



