530 A MANUAL OF BACTERIOLOGY 



pyriform bodies 2-4 /j. in length and 1-5-2 p. in largest diameter. 

 One end of each body is rounded, and the body gradually tapers to 

 a point at the other end, and the pair lie close together, their tapering 

 ends directed towards each other. A dark spherical body is present 

 at the rounded end of the parasite. 



Some of the young parasites exhibit amoeboid movements when 

 the blood is examined on a warm stage. In the internal organs 

 the parasites are more numerous ; in the kidney and liver 10-25 

 per cent, of the corpuscles contain them, in the heart-muscle 

 50 per cent. In the mild type 5-50 per cent, of the corpuscles in 

 the circulating blood may be infected at one time 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 p) 

 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 (Rhipi- 

 cephalus annulatus, R. australis). 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. 1 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. 2 



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 XXVI. a). 

 It is conveyed by the ticks Hcemaphysalis leachi in South Africa, 



1 See Smith and Kilborne, Texas or Southern Cattle Fever, United 

 States Dep. Agricult. Bull. No. 1, 1893. 



2 See Tidswell, Report on Protective Inoculation against Tick Fever, 

 New South Wales, Dep. Pub. Health, vol. i, 1898 ; vol. ii, 1900. 



