312 APPLIED BIOLOGY 



by the fact that their bodies consist of one cell. Any one- 

 celled animal is a protozoan (meaning first animal), and the 

 entire group of them is named Protozoa. There are numerous 

 species, but most of those known are like the amoeba and 

 paramecium in being of little interest except that study 

 of them has helped much towards explaining the life of higher 

 organisms, including man himself. However, a few proto- 

 zoans are now known to be of very great practical interest, 

 and some of these will be briefly described. 



274. Malarial Organism. Malaria in its severest forms 

 has long been one of the worst diseases affecting the human 

 race. Vast territories in some parts of the world have been 

 left practically undeveloped by civilized men because of 

 malaria. Little was known as to the cause of the disease 

 until after 1880, in which year a protozoan parasite was 

 discovered in red blood-cells. Before that time it was com- 

 monly supposed to be caused by some poisonous vapor or 

 miasm which arose from swampy land. In 1897, Ross, an 

 officer of the British army, demonstrated that the malarial 

 parasites first develop in the stomachs of certain mosquitoes 

 ( 329), from blood sucked from persons who have malaria; 

 and a year later other investigators showed that mosquitoes 

 which have obtained blood from a malarious patient are able 

 to transmit the parasites while sucking blood from perfectly 

 healthy persons. Many later studies have made it absolutely 

 certain that the Anopheles mosquito is the carrier of the dis- 

 ease ; and this is one reason for the recent attempts at ex- 

 terminating mosquitoes as far as possible. 



The effect of the malarial parasite upon the red blood- 

 corpuscles is as follows : Small bodies injected into the blood 

 by sucking mosquitoes attach themselves to blood-cells and 

 begin to burrow (they have amoeboid (amoeba-like) move- 

 ments). Within the blood-cell a parasite grows, at the ex- 

 pense of the cell, and soon divides into a number (6-24) of 

 small bodies called spores. Then the blood-cell disintegrates 



