INTRODUCTION 



197 



Many of these microorganisms absorb their nutrition directly from the 

 fluids of the tissues while others, amoebae, are able to devour cells. 



Protozoa are very much like all microorganisms in their manner of 

 living but there are details which belong to them as a class and should 

 be pointed out specifically. 



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FIG. in. A, Amoeba proteus; Na, a food particle; Cv, contractile vacuole; X, nucleus. 



(After Doflein.} 



'The ingestion of food is accomplished in some protozoa by 

 pseudopodia; the protozoon simply flows around and so encloses a food 

 particle (Fig. m). In the same way, these protozoa flow away from 

 waste particles which are to be eliminated. Other protozoa have defi- 

 nite mouth areas for the ingestion of food, and definite anal areas for 

 the discharge of residual material. Those protozoa which ingest solid 

 food, digest it within gastric vacuoles by the aid of enzymes and of 

 acids, just as is the case in many-celled animals. The most important 

 of the disease-producing protozoa live within nutrient fluids, for ex- 

 ample the blood, and they obtain their nourishment from the fluid in 



* Prepared by J. L. Todd. 



