172 INSECTS AND MAN 



of the parasite is unknown, though able scientists, aided 

 by most powerful microscopes, have tried to probe the 

 mystery. It is known, however, that these ticks, if trans- 

 ported to another host, can convey the germs of disease ; 

 and not only that, but the young generation, hatching from 

 eggs laid by an infected mother, are themselves infective 

 and can carry the disease. From what has been said it is 

 clear that cattle and ticks are necessary, in order that red 

 water may be perpetuated, and, so far as is known, no 

 other animal can replace either of them ; in fact, no animals 

 but cattle, deer, and buffaloes can be infected with the 

 disease. 



As we have already mentioned, dogs, sheep, and horses 

 all suffer from piroplasmosis, but the disease is peculiar to 

 each species, just as piroplasmosis of cattle is peculiar to 

 oxen and allied animals. For example, piroplasmosis in 

 cattle cannot be transmitted to horses, or vice versa, though 

 the disease can be, and is, easily transmitted from one ox 

 to another, or from one horse to another. The piroplasma 

 is pathogenic for one species of mammal only, and it requires 

 two animals a mammal and a tick for its complete life- 

 cycle, just as in the case of human malaria a human being 

 and a mosquito are necessary for the completion of the 

 malarial parasite's life-cycle. The tick Ixodes ricinus, 

 which, by the way, obtains its name from the fact that the 

 engorged female strongly resembles a castor-oil or Ricinus 

 seed, not content with transmitting red water in cattle, is 

 also, along with Dermacentor reticulatus (fig. 47) and Ixodes 

 hexagonus, the European vector of the parasites causing 

 piroplasmosis in dogs. In South Africa this disease is 

 transmitted by the tick Hceinaphy sails leachi, and in 

 India still another tick, Rhipicephalus sanguineus, carries 

 on the evil work. A closely related tick, Rhipicephalus 

 evertsi, is the African vector of piroplasmosis in horses, and 

 another, by name Rhipicephalus bursa, transmits the ovine 

 disease. In connection with piroplasmosis in sheep and 



