THEILEEIA. 297 



Sometimes cross-shaped forms are met with, but these are 

 regarded as aggregates of four parasites, and not fission 

 stages. The forms in the blood do not multiply by fission, 

 and are consequently assumed to be gametocytes. They 

 grow into adult gametocytes of two kinds — male gametocytes, 

 which are long, slender, " bacillary " forms, and female 

 gametocytes, which are plump, rounded or pear-shaped forms. 

 The gametocytes can only develop further in the tick, 

 Bhipicephaliis . 



Dimensions. — Schizonts 3-10/i in size ; gametocytes, rod- 

 like forms 2-5 fjb in. length by l'2fx. 



The Cycle in the Tick. — In the gut of the tick the gametocytes 

 leave the red corpuscles and develop into gametes. The 

 macrogamete is stationary, whilst the microgamete is motile, 

 seeks out the macrogamete, and is said to unite 'wdth it, 

 forming the zygote. The latter develops into a worm-like 

 ookinete, and no further development is known to take place 

 till after the moulting of the tick. After the moulting of the 

 tick, large cyst-like structures containing numerous nuclei 

 are met with in the salivary glands. Each cyst develops 

 a number of sporoblasts, and numerous very small sporozoites 

 are ultimately set free, which are introduced into the cattle 

 when the tick again sucks the blood. 



Bemarks. — The organism produces a serious disease of cattle, 

 known as East Coast fever, in various parts of Africa. It has 

 also been met with in Transcaucasia, Macedonia, and India. 

 The disease differs from that caused by Babesia higemina in 

 that hsemoglobinuria, jaundice, and progressive anaemia are 

 absent. Theiler (1904) demonstrated that East Coast fever 

 was a distinct disease, and that cattle which had recovered 

 from hsemoglobinuric fever due to Babesia were not immune 

 to it. He also found that the disease could not be transmitted 

 by inoculation of infected blood into a healthy animal. This 

 was explained as being due to the fact that the blood-forms 

 do not multiply. Experiments by Ed. Sergent and his co- 

 workers (1926) have, however, shown that this view is incorrect, 

 though, as Wenyon (1926) remarks, the occasional positive 

 results obtained by blood inoculations of healthy animals may 

 be due to the presence of endothelial cells in the peripheral blood. 



The blood -forms were carefully described by Nuttall, 

 Fantham, and Porter (1909) in artificial infections of animals 

 in England by means of ticks, Bhipicephalus evertsi, imported 

 from South Africa ; and also by Nuttall (1913). The life- 

 history was studied by Gonder (1910, 1911 a, 1911 6), whose 

 account has been followed above, but certain points lack 

 confirmation. 



Lingard (1907) and Gaiger (1910) recorded this species 

 from India, but no one seems to have seen it since. 



Habitat. — Blood of ox, Bos taurus Linn. (?) : India. 



