THE PATHOGENIC PROTOZOA 177 



refractory. There is no evidence that a previous attack 

 of sleeping-sickness gives any immunity. Trypanosomes 

 surviving medication with arsenic compounds acquire 

 a tolerance of them. 



Trypanosoma Brucei. Domesticated horses, cattle, and 

 dogs entering a ' fly country ' are liable to nagana, or 

 ' fly disease,' the aetiological agent of which is T. Brucei. 

 This parasite has a somewhat slender, spindle-shaped body, 

 about 15 ILL to 20 JLI in length, bluntly pointed posteriorly, 

 and prolonged into a long, delicate flagellum at the 

 anterior end. On one aspect of the organism is a delicate, 

 undulating membrane, commencing near the posterior 

 extremity at a micro- nucleus, or blepharoblast, and becom- 

 ing prolonged into the flagellum. Near the centre of the 

 organism is a macro-nucleus, and the protoplasm is refrac- 

 tile and finely granular, and contains a vacuole. The 

 appearance of this hsematozoon in the blood is signalised 

 by a rise in temperature; the incubation period is from 

 seven to twenty days, after which period the hsematozoa 

 may be found swimming actively among, and apparently 

 ' worrying,' the corpuscles, red blood-corpuscles becoming 

 very largely reduced in numbers. G. morsitans transmits 

 the parasite. Wild game harbour the parasite without 

 showing any sign of the disease in a happy expression 

 of Bruce, they act as ' reservoirs,' and removal of the big 

 wild herbivora from a district considerably lessens the 

 incidence of the disease. 



Trypanosoma Evansi is found in surra, a disease of 

 horses and camels in India. The parasite is more active 

 than T. Brucei, but is regarded by some as identical 

 with it. 



Trypanosoma equinum occurs in an equine disease 

 prevalent in South America, mal de Caderas, the prominent 

 symptom of which is paralysis of the hindquarters. 



Trypanosoma dimorphon, or dimorphum, occurs in a 

 trypanosomiasis of horses in Senegambia. Two forms, 

 long ands hort, occur, and by the prolongation of the 

 protoplasm to the tip of the flagellum a free process is 

 eliminated. 



Trypanosoma Theileri measures up to 65 //. in length, 

 and is found in South African cattle affected with galziekte. 



Trypanosoma Transvaaliense measures up to 50^ long 

 and up to 6^ thick. It is found in South African cattle. 



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