PATHOGENIC PROTOZOA. 



Protozoa are unicellular animal organisms. They are 

 attracting ever increasing attention since they have been 

 found to play a very important part in the causation of dis- 

 eases, particularly of diseases peculiar to tropical countries, 

 and as they are studied by methods that have much in common 

 with those used for the bacteria they may be considered here 

 briefly. Protozoa are numerous in pond and ditch water, 

 and these species seem to be harmless. However, many 

 diseases of the lower animals are caused by protozoa, such as 

 surra, Texas fever and coccidium disease of rabbits. Birds,* 

 reptiles and frogsf may show organisms in the blood resem- 

 bling the parasites of malaria. Until recently it has been 

 doubtful whether any pathogenic protozoon has ever been 

 propagated in pure culture outside of the body of the host. 

 This has been accomplished by Novy and MacNeal for a 

 parasite (Trypanosoma) from the blood of the ratj and from 

 many species of birds§ on rabbit-blood-agar. 



Novy 1 1 gives the following classification of the pathogenic 

 protozoa which are of most interest: Trypanosomata, met 

 free in the blood plasma; hemocytozoa, found in the blood- 

 cells, represented by the malarial parasite in man and by 

 related organisms in the lower animals, also by the piro- 

 plasmata found in Texas cattle fever and allied affections; 

 amebse, found in the intestines in dysentery and elsewhere. 

 Other forms of pathogenic protozoa have been recognized, 



*Opie and MacCallum. Journal Experimental Medicine. Vol. III. 



fLangmann. New York Medical Journal. January 7, 1899. Williams 

 and Lewis. 



tNovy and MacNeal. Contributions to Medical Research. Dedicated to 

 Victor C. Vaughan. 1903. , „. , ^ , , ,■ 



§Novy and MacNeal. On the Trypanosomes of Birds. Journal of In- 

 fectious Diseases. Vol. II., No. 2. p. 257. March, 1905. 



WReyTmtiromJourn.Am.Med.Assn. Jan. 5 and 12, 1907. Vol. XLVIII. 



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