MICROBES— INFECTION— IMMUNITY 447 



Protozoa. — Protozoa are unicellular organisms of the 

 animal kingdom. During the last few years they have 

 attracted a great deal of attention, as many have been 

 found in connection with well-known diseases. 



The following grouping of the protozoa is adopted : 



(Rhizopoda. 

 ISIastigoplwra {flagellated "protozoa). 

 Sporozoa. 



„.,. , [Ciliata. 



Ciliophora. ] „ 



'^biictona. 



Rhizopoda. — To this class belongs the Amceha coli found 

 in the intestine of man, and believed to be one of the 

 causes of dysentery. 



Mastigophora. — The flagellated protozoa have their most 

 interesting representative in the Trypanosomata, a family 

 which recently has become of the greatest importance as a 

 cause of specific disease of both man and animals. Several 

 species of Trypanosoma are known. T. Evansi causes 

 ' surra,' the well-known disease of horses in India. 

 T. Brucei is found in the African Tse-tse fly disease, and is 

 transmissible by means of the inoculation of this fly to all 

 domesticated animals. The fly obtains the organism from 

 big game; the latter seem to be immune, and suffer no incon- 

 venience from the presence of this organism in their blood. 

 The T. equinum is found in South America, and is the 

 cause of a horse disease known as ' mal de caderas ' ; the 

 T. equiperdum has been found in Algeria and India, and is 

 connected with the venereal disease of equines known as 

 ' maladie du coit ' or ' Dour in e.' Another South African 

 trypanosome is the T. Theileri, found exclusively in 

 cattle, and causes one of the forms of so called ' gall 

 sickness.' With the exception of T. equiperdum, which is 

 communicated by coitus, all the others named are conveyed 

 by biting insects (see p. 425). 



There has recently been found a new trypanosome in 

 the blood of horses in Gambia, which produces anemia, 

 and another is found in the blood of men in Central 



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