Chapter 1 

 Introduction 



UNFORTUNATELY mail is liost to soiiie twenty-seven spe- 

 cies of parasitic organisms that are known as protozoa 

 or unicellular animals. These protozoa nourish themselves 

 b\' absorbing the body fluids or by feeding directly on 

 tissue cells or on solid particles present in the digestive 

 tract. The\' grow and multiph' and the daughter indi\iduals 

 in turn grow and multiph-. This phase of a protozoan is 

 called the trophozoite or vegetative stage (Fig. 1, i^). 



The bodv of a trophozoite is made up of the nucleus and 

 cvtoplasm. The nucleus is vesicular in stiaicture, except in 

 Balantidium coli, a ciliate, in which the macronucleus is a 

 large compact one (Fig. 13, ^). The xesicular nucleus (Fig. 

 1, 2-4) is composed of the nuclear membrane which en- 

 closes the nucleoplasm. The chromatin granules are either 

 attached to the inner surface of the membrane or sus- 

 pended in the nucleoplasm. In addition there is usually an 

 endosome which is a conspicuous bod\^ and stains difi^er- 

 ently in various protozoa. The endosome is either sus- 

 pended in the nucleoplasm or attached to the nuclear 

 membrane. 



The cytoplasm is frequenth differentiated into an outer 

 layer, the ectoplasm, and an inner mass, the endoplasm 

 (Fig. 3, i> 2). The nucleus, food vacuoles, etc., are ordinarily 

 located in various parts of the endoplasm. In Sarcodina, 

 Flagellata, and Ciliata, the trophozoite mo\es about ac- 



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