MICEOBES— INFECTION— IMMUNITY 449 



infection of the animal body, but solely for the reproduction 

 of the species, and this stage only occurs in the intermediate 

 host. The conjugation of the two elements is called the 

 Oocyst, which develops the spores, hence the name of this 

 stage. 



The best known pathogenic species is the Coccidium 

 cunicoli which lives in the liver of rabbits. A similar 

 coccidium is probably the cause of the hsemorrhagic 

 diarrhoea of cattle, described in Switzerland as ' die rote 

 Ruhr ' or red diarrhcea. This disease is generally observed 

 during the summer, and is attributed to the cattle grazing 

 on fresh grass, and drinking stagnant water. 



Young sheep and goats may suffer from an enteritis due 

 to coccidisB ; dogs, cats, and poultry, are also known to be 

 affected by this organism. 



The intra-corpuscular parasites of the blood belong to 

 this group ; they are spoken of as Hcemosporidia, and 

 include the parasites of human malaria, viz. Plasmodium 

 IwcBcox the cause of tropical fever ; P. vivax found in 

 tertian fever, and P. malaria found in quartan fever. A 

 somewhat similar parasite may be found in birds, the 

 Hcemoproteus Danileivsky. The schizogenic stage of this 

 organism takes place in the blood of the host, while the 

 sporogenic stage occurs in the body of a mosquito of the 

 species Culex. 



Another important genus belonging to the group of 

 hasmosporidia, and the one which most interests us, is the 

 Pyroplasma, of which the best known, perhaps, is the 

 P. bigeviinum the cause of Texas fever; but there are 

 several others, all pathogenic: the P- cariis produces 

 malignant jaundice of the dog ; the P. eqtii is the cause of 

 biliary fever in horses, mules, and donkeys ; the P. ovis 

 has been discovered in the disease of sheep known in 

 Eoumania as ' carceag ' ; the P. Ugeminum causes the 

 hffimoglobinuria of European cattle, which is probably 

 identical with that found in Texas fever, while the formid- 

 able African Coast fever (Ehodesian redwater) of cattle, is 

 caused by a very small pyroplasma, described by Koch as 



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