ONE-CELLED ANIMALS— PHYLUM PROTOZOA 97 



word "malaria" comes from two combined words meaning "bad air," 

 a derivation that goes back to a time when the disease was attributed 

 to the damp night air. We now know that it is the mosquitoes which 

 are likely to be out in the night air that spread malaria. This is one of 

 the best understood, yet one of the most destructive, diseases in the 

 world today. We know how it is spread, how to treat it successfully, 

 and how to prevent it, but it still ranks as the most serious infectious 

 disease on our globe. Millions die from it each year, and many other 

 millions are incapacitated by it. There are large sections of the world 

 which are practically uninhabitable by white persons because of it. 

 Our armed forces in the South Pacific found malaria a more serious 

 enemy than human enemies. Large numbers of highly trained fighting 

 men died or were disabled by this disease without ever going into 

 action. We were successful in our operations in this region only be- 

 cause of the splendid work done by the entomologists and medical men 

 in preventing and combating the infection. 



At one time there were large sections of our own country where 

 malaria was very prevalent, but today the spread of this disease has 

 been reduced to the vanishing point in the continental United States. 

 In spite of new cases being brought in from foreign countries, the 

 vigorous program of the public health departments plus the prompt 

 use of new anti-malarial drugs keeps the disease suppressed. 



There are several types of malaria caused by different species of 

 malarial parasites, but the one most prevalent and once common in our 

 southern states is tertian malaria, which is caused by Plasmodium vivax. 

 The word "tertian" means third, and this name was chosen because the 

 chills and fever tend to reappear every 48 hours. By an old Roman method 

 of reckoning, it was customary to count the day that something happened 

 as the first day, the day following as the second, and the day following that 

 as the third. Thus, even though the chills were only two days apart, they 

 were said to recur on the third day. 



Infection in a person may result through the injection of spores that 

 are present in the saliva of an infected mosquito. The injected spor- 

 ozoites enter cells lining the capillaries of the liver, spleen, and other in- 

 ternal organs. There they multiply for about a week or ten days 

 and then break out into the blood stream where they attack the red 

 blood cells. Each sporozoite may enter a red blood cell. There it 

 rounds itself up into a ball with the nucleus at the edge and a vacuole 

 in the center that makes it look like a signet ring. This is called the 

 signet-ring stage. It gradually fills in the inside of the ring and takes 

 on an amoeba-like form that now fills the center of the red blood cell. 

 Then it breaks up into between 15 and 20 spores, the merozoites. The 



