PROTOZOA 



185 



Euglena ; F, flagel- 

 lurii; iV, nucleus; 

 Pv, contractile 

 vacuole. 



chlorophyll, while others appear to take in food in the same manner as animal 

 cells. They have a red pigment spot at one end of the cell body. This spot 

 is sensitive to light, hence it has been called an eye- 

 spot. A common flagellate is called Euglena. The green 

 color of stagnant pools is due to the presence of enor- 

 mous numbers of this organism in the water. 



Relation of Protozoa to Disease. — The study of 

 the life history and habits of the Protozoa has resulted in 

 the finding of many parasitic forms, and the consequent 

 explanation of some kinds of disease. One parasitic pro- 

 tozoan, like an amoeba, is called Plasmodium malarice. It 

 causes the disease known as malaria. Part of its life is 

 passed within the body of a mosquito (the anopheles), 

 into the stomach of which it passes when the mosquito 

 sucks the blood from a person having malaria. Within 

 the body of the mosquito a complicated part of the life 

 history takes place, which results in a stage of the para- 

 site establishing itself within the glands which secrete 

 the saliva of the mosquito. When the mosquito pierces its human prey a 

 second time, some of the parasites are introduced into the blood along with 

 the saliva. These parasites enter the corpuscles of the blood, increase rap- 

 idly in size, and then form spores. The process of spore formation results 



in the chill of malaria. Later, 

 when the spores almost fill the 

 blood corpuscle, it bursts, and the 

 parasites enter the blood. There 

 thej^ release a poison which causes 

 the fever. The spores may again 

 enter the blood corpuscles and in 

 forty-eight or seventy-two hours 

 repeat the process thus described. 

 Another group of piotozoan 

 parasites are called trypanosomes. 

 One of this family lives in the 

 blood of native African zebras 

 and antelopes; seemingly it does 

 them no harm. But if one of 

 these parasites is transferred by 

 the dreaded tsetse fly to one of 

 the domesticated horses or cattle 

 of the colonist of that region, 

 death of the animal results. 

 Another fly is believed to carry a specimen of trypanosome to the natives 

 of Central Africa, and to cause " the dreaded and incurable sleepii-g sick- 



BIoolI corpuscles of a patient with malarial 

 fever. Two corpuscles contain the para- 

 sites. Photograph, greatly enlarged, by 

 Davison, 



