If a drop of blooddrawn from a malarial patient is exposed 

 to the air for 10-30 minutes, some of the Plasmodium spores 

 are observed to put out little whip-like processes which usu- 

 ally break off and swim about j:by themselves while other 

 spores remain round and motionless. The former 

 (microg-ametes) unite with the latter — (macrogametes. ) 

 This strange development of the Flasmodimn spore 

 was found to take place only when outside of the body 

 of the patient, and it was therefore recognized as the begin- 

 ning of an extra-corporeal stage of the existence of the para- 

 site. 



In what host was this period of its life history passed? 

 Since the malarial parasite is entirely unable to leave the 

 blood of its own accord the question became — what agent 

 could remove it? Clearly some blood-sucking animal com- 

 mon in low-lying, damp regions, probably a suctorial insect, 

 w^as the culprit. Suspicion at once pointed to the mosquito. 

 Finally by the labor of Laveran, Major Ross in India, and 

 Koch, Grassi and others elsewhere, the surmise was proved 

 orrect, and the complete life history of Plasmodium made 

 out. 



It was found that in the digestive tract of the gerus 

 Anopheles, the same development of the Plasmodium spore 

 into conjugating micro — and macrogametes takes place as 

 has been observed in the drop of blood drawn from the body 

 of a malarial patient. The fertilized egg which is the result 

 of this union bores through the stom.ach wall of the mos- 

 quito and out in the body cavity breaks up into a host of 

 spores. These work their way forward into the salivary 

 glands of the insect, and here lie ready to be trans- 

 ferred to the blood of the next victim of the mosquito. 

 The entire process of development which the parasite under- 

 goes while enjoying the mosquito as a host occupies seven or 

 eight days. 



That the malarial parasite is transmitted solely through the 

 agency of mosquitoes has been strikingly demonstrated by ex- 



22 



