202 



PARASITISM 



hydrophobia, presumably by the secretion of some toxic substance, 

 causes the destruction of brain and nerve cells, while Cytorydes 

 variolce produces a like destruction of the generative cells of the skin. 

 A much more subtle action is shown by those parasites which 

 cause hypertrophy or multiplication of the infected cells. The great 

 tumors often found in the cruciferee arising from the root cells owe 

 their origin to some chemical effect produced by the intracellular 

 parasites Plasmodiophora brassicce, and numerous observers have 

 sought to explain human cancer and other tumors in like manner. 



FIG. 84 



n 



^sK^^v^s^. * /^u) / x 



^li^^^^m^fe^^ 



^M "*KfeC5' ^J? ;?^ /(*&'?,,*<$-, 



*c/. V j-Tr t uj rS^-^ !ioi ' 4 .TOTs^> * _ i ?? ^ ^Jt-r 



Caryotropha mesnili, Sied. 4, coecidian parasite of spermatogonium cell which is much 

 hypertrophied while the remaining spermatogonia of the bundle form an epitheliod layer about 

 it. An intracellular canal in the parasite connects the nucleus (n) of the host cell and the 

 nucleus of the parasite while a stream of foodstuff proceeds from the former to the latter. 

 (After Siedlecki, combination of drawing and photograph.) X 760. 



The demoralizing effect which an intracellular parasite has upon 

 an animal cell is well shown by Siedlecki in the case of the sporozoon 

 Caryotropha mesnili. The organism is a parasite in the spermato- 

 gonia of the annelid Polymnia nebulosa, where the sperm cells are 

 aggregated in bundles, in the characteristic annelid fashion, usually 

 about a feeding mass or blastophore. The parasite gets into such a 

 cell as a merozoite or sporozoite, one only of the bundle, as a rule, 

 being infected, and as it grows the nucleus of the cell is displaced to 

 one side and the cell loses its characteristic germinal structure, becom- 

 ing hypertrophied and distorted (Fig. 84). Not only the infected cell, 

 but all of the other cells of the spermatogonia bundle are affected, 

 and none of them continue the normal development, but become 

 arranged like epithelial cells about the hypertrophied infected cell. 



