278 BACTERIOLOGY FOR NURSES 



become again suitable the organism absorbs water, the cyst wall 

 ruptures, and ordinary development is recommenced. 



Nutrition and Reproduction. Many of the protozoa obtain 

 their nourishment by the absorption of the fluid food directly 

 through the cell wall ; others are able to ingest solid particles, 

 such as bacteria, through a suctorial tube or, as amongst the ameba, 

 by extending a portion of their protoplasm and completely sur- 

 rounding the food morsel. After the food is digested the waste 

 substance may be excreted by osmosis or by means of a contractile 

 vacuole. 



The simplest form of reproduction is by transverse or longitudinal 

 division. A more complex form, spoken of as multiplicative 

 reproduction, or brood formation, occurs, in which the nucleus 

 divides into several portions, each of which becomes surrounded 

 with protoplasm and finally separates into as many daughter 

 cells. Multiplicative reproduction without conjugation is spoken 

 of as schizogony and the daughter cells are known as merozoites ; 

 when after fertilization such division takes place within a cyst 

 it is spoken of as sporogeny and the resulting cells are called 

 sporozoites. 



Many forms multiply both sexually and asexually, some of 

 which pass the sexual phase of their existence in one host and the 

 asexual phase in another. 



The forms already studied that are pathogenic for man are 

 included in four main classes : 



1. Rhizopodia. Movement by means of temporary protrud- 



ing portions known as pseudopodia; reproduction 

 by simple division or multiplication within a cyst; 

 possession of one or more nuclei. Genus parasitic for 

 man. Entameba. 



2. Flagellata. Movement by means of flagella; possession 



by certain forms of nucleus, contractile vacuoles, and a 

 small opening for food. Genera parasitic for man. 

 Trypanosoma, Leishmania. 



3. Sporozoa. May form pseudopodia; food ingested by 



osmosis; one or more nuclei; no contractile vacuole; 



