PROTOZOA AND DISEASE 



H5 



Remains of siliceous Radiolarian shells are known from Silurian 

 and from Devonian strata onwards. From the later Tertiary deposits 

 of Barbados earth, Ehrenberg described no fewer than two hundred 

 and seventy-eight species. 



Protozoa and Disease. — The discoveries of recent 

 years have shown that the study of Protozoa is an inquiry 

 of great practical importance. All three main divisions 

 of the Protozoa contain important disease-producing 

 parasitic forms, especially the flagellated Infusorians 

 called Haemoflagellata (Trypanosomes) and the Sporozoon 



Fig. 67. — Glossina palpalis, tsetse fly. 



group of Haemosporidia, to w^hich Plasmodium vivax (see 

 Fig. 68) belongs. 



I . Various species of Amoebae are parasitic in the human 

 food canal, e.g. Entamoeba colt, E. histolytica, lodamoeba 

 butschlii, Endolimax nana, and Entamoeba gingivalis in 

 ill-kept teeth, but the only pathogenic form is Entamoeba 

 histolytica. This Amoeba eats into -the wall of the lower 

 intestine, causing ulceration and, in severe cases, amoebic 

 dysentery as well as abscesses on the liver and elsewhere. 

 A clear cyst may be formed within which the nuclei divide 

 usually into four. The cyst is passed out of the intestine, 

 and should it find its way into the food canal of another 

 human being, the cyst breaks and sets free the contained 

 daughter Amoebae. 

 10 



