THE PROTOZOA AS PARASITES OF 



MAN 



The interest which the study of the Protozoa has for mankind 

 is not merely theoretical, in virtue of the remarkable pecuHarities 

 of their organisation, but is very near and practical, by reason 

 of the fact that a number of them live in the bodies of man, 

 and that there they sometimes cause serious diseases. In this 

 chapter we shall study briefly examples, drawn from all the four 



Fig. 34. — Entamoeba, x c. 1000. — After Fantham. 



A, E. coli ; B, E. histolytica. 

 b.c, Ingested red blood corpuscle ; f.v., food vacuole ; nu., nucleus 



ps., pseudopodium. 



classes of the group, of which man is a host — that is, which he har- 

 bours as parasites. In so doing, our attention must be given both 

 to facts which, directly or indirectly, are of medical importance, 

 and to others which have wider biological significance. 



ENTAMCEBA 



The several kinds of Entamoeba (Fig. 34) differ from Amoeba 

 in that they have no contractile vacuole.^ They have one or two 

 large blunt pscudopodia, chiefly composed of ectoplasm, and they 

 are all parasites, usually in the alimentary canal of one of the 

 vertebrate animals. E. coli is about 20-30 /x in diameter, and lives 

 in the upper part of the large intestine of man, feeding upon 

 the bacteria which infest that region, and also upon the remains 



' A contractile vacuole has been found in one organism which has been classed 

 with the Entamcebts. 



6a 



