THE PROTOZOA AS PARASITES OP MAN 



145 



In this the nucleus, after proceedings in which some of 

 its chromatin is lost, while a large vacuole temporarily 

 appears in the cytoplasm, forms eventually two nuclei 

 while a cyst is being secreted around the body. The 

 two nuclei in the cyst divide into eight. The ordinary 

 Entamoeba die in the feces. So also do the cysts unless 

 the feces dry, but in the latter case they are distributed as 

 dust, and if they thus reach water or human food and are 

 swallowed by a man the cysts germinate in the intestine of 

 the new host, the protoplasm dividing and emerging as 



Fig. 88. — Entamceba. — After Fantham. 

 A, E. coli\ B, E. dysenteries. 



i.e., Ingested red blood corpuscle ;f.v., food vacuole ; mi., nucleus ; 

 ps., pseudopodium. 



little individuals each with a nucleus. By these the cycle 

 is re-started. 



Entamceba dysenteries, sometimes known as E. histolytica, 

 also inhabits the human intestine. It varies much in size 

 but reaches greater dimensions than E. coli, from which 

 it also differs in being more active, having a distinct ecto- 

 plasm over the whole surface of the body, and taking up 

 strongly, while still alive, the stain known as "neutral red." 

 Unlike E. coli it bores through the mucous membrane of 

 the intestine. This it does by making its pseudopodia of a 

 sharper shape. It then penetrates the blood vessels in the 

 same way, and is carried by the circulation to the liver, 

 where it may set up abscesses. Its action on the intestinal 

 wall causes dysentery. It feeds not only on bacteria but also 



