THE PIROPLASMATA 655 



or another, and the parasite appears in some cases as a coccus-like 

 body at the periphery of the corpuscle. This appears to become 

 enlarged and spindle-shaped, then to taper in the middle, divide, 

 and so give rise to the pyriform bodies. Occasionally minute 

 free coccoid bodies are seen in the plasma, and at times two to five 

 minute (0-5/i) coccoid cells are present in the red cells. After 

 death the pyriform bodies seem to become spherical or angular. 



Sexually differentiated gametes are not known with certainty 

 but flagellated forms have been described. 



The disease is transmitted through the bites of ticks (ETiipi- 

 cephalus annulatus, B. austmlis). The female tick, after biting an 

 infected ox and sucking its blood, falls off and lays its eggs ; the 

 eggs hatch in two to six weeks' time, and the daughter ticks 

 transmit the disease to other animals through their bites. The 

 disease may be to some extent controlled by prophylactic measures 

 designed to destroy the ticks, and to prevent infection thereby. 



A partial immunity is enjoyed after an attack of the disease, 

 but by repeated attacks the immunity may be rendered absolute. 

 By inoculation with the blood of an affected animal in which the 

 fever has subsided, a transient illness in the inoculated animal 

 is produced together with partial immunity, and by a second 

 or third inoculation the immunity may be much increased. The 

 mortality from such a procedure amounts to 3-5 per cent. 



P. parvum causes Rhodesian red -water of cattle. It is not 

 directly inoculable, and is conveyed by the tick R. appendiculatus. 



P. equi causes biliary fever in horses. 



P. canis causes epidemic jaundice in dogs (Plate XXXI, a). 

 It is conveyed by the ticks Hcemaphy sails leachi in South Africa, 

 R. sanguineus in India, and Dermacentor reticulatus in Europe. 

 (On Ticks, see Nuttall and others, in Journ. of Hygiene, vol. iv 

 et seq., and Parasitology, vol. i et seq.) 



Haemogregarina 



The Hsemogregarines (which must be distinguished from the 

 Gregarines) are unpigmented parasites, not amoeboid, typically 

 having an elongated body or vermicule, occurring in the blood, 

 mostly in cold-blooded vertebrates, but several species have of 

 late been found in mammals (dog, jerboa, palm squirrel), though 

 not in man. In the dog, the parasite (Leucocytozoon canis} occurs 

 as an elongated, curved or doubled-up body in the polymorpho- 



