174 AIDS TO BACTERIOLOGY 



CHAPTER XVII 

 THE PATHOGENIC PROTOZOA 



THE Protozoa are unicellular organisms belonging to the 

 animal kingdom. Reproduction generally takes the forms 

 of simple fission and spore formation, but complex life- 

 cycles, involving the alternation of sexual and asexual 

 phases, occur in some. A conjugation of two dissimilar 

 cells (gametes) may take place to form a zygote. Gametes 

 fulfilling a duty analogous to that of spermatozoa are 

 called microgametes, the other variety being macrogametes. 



The following is one classification of the Protozoa: 



Sarkodina. The Amoebae, the only type of this division 

 parasitic for man, have no cell-wall, movement is slow, 

 and takes place by the projection of temporary limb -like 

 processes (pscudopodia). Multiplication is by fission or 

 spores. 



Mastigophora. Flagellated forms, including trypano- 

 somes and probably spirochsetes. 



Sporozoa. Passive and exclusively parasitic organisms, 

 reproducing by spore formation, including malarial para- 

 sites, Coccidium and Piroplasma. 



Infusoria. Actively motile ciliated protozoons, with 

 definite cell-walls, and small micronucleus participating 

 in conjugation, and a vegetative macronucleus. Includes 

 Balantidium. 



Parasitic Amcebse. 



Three Amrebse, known as Entamcebse, are parasitic for 

 man: 



Entamoeba buccalis occurs in dental caries. 



Entamoeba coli is an apparently harmless, and not 

 infrequent, inhabitant of the bowel. 



Entamoeba histolytica is found in the faeces in the form 

 of chronic dysentery common in the tropics, and in the 

 pus of tropical abscess of the liver, a not infrequent 

 sequela of this form of dysentery. A. histolytica measures 

 about 15 /LI to 50// in diameter. The pseudopodia are short 

 and blunt, and vacuoles, a nucleus, and highly refractile 

 granules are to be seen in the endosarc, often together 

 with blood-corpuscles, pus cells, and bacilli. Amrabae can 

 be separated from ingested bacteria by a 20 per cent. 



