— 12 — 



Anopheles as a second or intermediate host of the malarial organism was worked] 

 out later by Doctors Alanson and Ross. (A full account of the discovery will be 

 found in Kellogg's American Insects, and it is unnecessary for me here to describe 

 the difficulties that were met and overcome). 



The malarial mosquito {Anopheles) : (a) male ; 

 (b) female, enlarged. 



The malarial plasmodium on gaining access to the human body lives within 

 a red blood-corpuscle and thrives at the expense of the haemoglobin. A char- 

 acteristic excretory product in affected cells is the black granules of melanin. In 

 48 hours the plasmodium reaches maturity and divides into many spores, termed 

 fnerozoitcs, which are set free in the blood. These soon enter new blood-corpus- 

 cles and reach maturity in 48 hours as before. This production of spores coin- 

 cides with the characteristic "chill" of ague, and is followed by a fever when the 

 spores enter the blood-corpuscles. As a result of the destruction of the red 

 blood-cells the patient becomes anaemic. Certain of these spores, however, 

 make no attempt to enter new blood-corpuscles and may remain in the blood for 

 an indefinite period. These are the gametes — the micro and macro-gametes — 

 which, if taken into the stomach of an Anopheles mosquito, will, however, undergo 

 further development. The male or micro-gamete produces a number of whip- 

 like threads or flagcllae, which are capable of uniting with the female or macro- 

 gametes, producing vermicules or ookinetes. These penetrate into the wall of the 

 stomach of the mosquito where they rest as cysts, forming little lumps on the 

 outer surface. These cysts mature in about ten days and burst, liberating large 

 numbers of ^/'oro-blasts into the body cavity, Avhence they find their way to the 

 salivary glands. When such an affected mosquito bites a human being these 

 spores are injected into the blood and enter the red corpuscles. It will be seen, 

 therefore, that ordinarily the Anopheles mosquito is the only agency for the 

 transmission of malaria to man. 



Stegomyia Mosquito and Yellozu Fever. 



The demonstration of the causal relation between Stegomyia mosquito and 

 Yellow fever is another interesting story, and was worked out mainly by Major 

 Walter Reed of the U. S. Army Medical Service in Cuba in 1900 and 1901. In 



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