482 THE CONTROL OF MALARIA AND YELLOW FEVER 



ing many of these small swellings in the stomach of the mosquitoes 

 and found that they contained numerous parasites. When the 

 swellings reached a certain size they would burst and the parasites 

 were scattered through the mosquito's body. Some entered the 

 salivary glands. Ross concluded that these parasites in the saliva 

 of the mosquito would pass into the blood of the bird when the 

 mosquito bit the bird. 



Cause. ]Malaria is caused by a protozoan parasite, Plasmodium 

 malariae, somewhat hke the amoeba. It has two hosts : the 

 female mosquito of the genus Anopheles, and man. There are 

 really three different types of malaria, caused by three different 

 but related microorganisms. Malaria occurring in our latitude is 

 a mild form of the disease. 



Spread. The germ of the disease is spread by the bite of the 

 female Anopheles which has previously bitten a malarial patient. 

 (The male feeds on plant juices.) The common mosquito, 

 of the genus Culex, does not transmit malaria or yellow fever. 



Life history of the malaria parasite, Plasmodium malariae. The 

 amoeba-like organism of malaria cannot complete its life history 

 in the blood stream of man alone ; it requires two hosts, the mos- 

 quito and man. Germs are injected into man through the bite of 

 an infected mosquito. They enter the red blood corpuscles and 

 multiply there, finally forming from six to sixteen spores. At inter- 

 vals of 24, 48, or 72 hours, depending on the type of malaria, the 

 spores, having destroyed the corpuscle, escape into the blood 

 stream. The sudden release of these poisons, and the subsequent 

 rallying of the body in an effort to counteract them, are thought 

 to cause the chills and then the fever which are characteristic of 

 malaria. 



Each escaped parasite now fastens itself to another red cor- 

 puscle, enlarges, forms spores, and having used up and disinte- 

 grated the corpuscle, again is set free, not as one but as many 

 parasites. The cycle is repeated over and over again, until the 



