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TEXTBOOK OF ZOOLOGY 



dition the parasite divides by binary fission into first two, then four, 

 and finally (in E. coli) eight little amoebae. If the cyst is swallowed 

 by another host, the cyst wall is dissolved and the four or eight 

 young amoebae come out to begin the active stage again. The com- 

 mon Endamoebae of man are E. gingivalis which lives in the mouth 

 and is usually transmitted by kissing, and the two intestinal species 

 E. coli (nonpathogenic) and E. histolytica. The latter species breaks 

 down the cells of the intestinal lining by means of enzymes which it 

 secretes, and then ingests the broken cells in the same way that the 

 common free-living amoebae take in their food. The disease caused 

 by E. histolytica is known as "amoebic dysentery." Infection occurs 

 as the result of eating food or drinking water which has been con- 

 taminated by the feces of infected people, as in the case of the 



Fig. 392. — Endanioeba coli. A, stained vegetative amoeba; B, cyst witli eight 

 nuclei, n., nucleus, showing coarse peripheral chromatin granules, chromatin 

 granules in "clear zone" between periphery and kai-yosome which is eccentric in 

 position ; chr.b., remnant of chroniatoid body. Numerous food vacuoles in vegeta- 

 tive form. (Reprinted by permission from Introduction to Human Parasitology by 

 Chandler, published by John Wiley and Sons, Inc., after Dobell.) 



Chicago hotels where contamination of drinking water by water 

 siphoned up from the toilet drains into the water pipes caused a 

 serious outbreak in 1933. 



The malaria parasites, of which there are three species infecting 

 man (Plasmodium vivax, P. falciparum, and P. malariae, each caus- 

 ing a different form of malaria), are Protozoa belonging to the class 

 Sporozoa, and are very highly modified for parasitic life. The 

 adaptations for parasitism and for transmission from host to host 

 involve a very complex life cycle. The two main phases of the life 



