PIROPLASMOSIS 569 



long and varying in breadth. The peripheral part is denser than the 

 central, which often appears as if vacuolated, and at the broad end there 

 is a well-staining chromatin mass. Sometimes irregular and ring-, rod-, 

 or oval-shaped individuals occur. The organisms are found within the 

 red blood corpuscles of the infected animal and also free in the blood. 

 In the former situation there is sometimes only one within a cell, but 

 the numbers vary under different circumstances and in different species. 

 Multiplication takes place by fission, and the new individuals, remaining 

 for longer or shorter times in apposition, account for some of the 

 appearances seen in cells. Especially in the forms free in the blood 

 pseudopodial prolongations of the protoplasm, usually from the pointed 

 end, are developed, and it may be by means of such pseudopodia that 

 entrance to the red cells is obtained. Infection is usually carried from 

 infected animals by means of ticks. In one case Koch has described the 

 development in the organism, in the stomach of the tick, of spiked proto- 

 plasmic processes sprouting out from the broad end of the piroplasm, 

 and the occurrence of conjugation of two such individuals by their 

 narrow ends to form a zygote. Further observations, however, here are 

 necessary, and nothing is known of the further history of the parasite 

 within the insect except that the eggs in the ovary may become infected, 

 so that insects developed from these can carry infection to animals. 

 Frequently when an animal has passed through an attack of a piro- 

 plasmosis it is immune to the disease, and with regard to this immunity 

 in certain cases very interesting facts have been observed. For instance, 

 the condition may not be associated with the disappearance of the 

 parasite from the blood of the immune animal, and the latter may thus 

 be a source of danger to other non-immune animals with which ticks 

 harboured by it may come in contact. 



The following are the chief piroplasmata causing disease in animals : 

 (1) Piroplasma bigeminum. This was first described by Theobald Smith 

 and is the cause of Texas or red-water fever, a febrile condition associated 

 with h'semoglobinuria, which occurs in the Southern States of America, 

 the Argentine, South and Central Africa, Algeria, various parts of 

 Northern Europe, and in Australia. The organism gets its name of 

 bigeminum from the fact that it is often present in the red cells in pairs, 

 which may be attached to one another by a fine thread of protoplasm ; 

 this probably results from the complete separation of two individuals 

 being delayed after division has occurred. Infection is here spread by 

 the tick boophilus bovis, and some of the characteristics of the disease 

 epidemiologically are explained by the fact that this insect goes through 

 all its moultings on the same individual host. (2) Piroplasma parvum. 

 This organism was discovered by Theiler in the blood of cattle suffering 

 from African East Coast fever, a disease closely resembling Texas fever, 

 which prevails endemically in a narrow strip along a long extent of the east 

 coast, and which occurs epidemically inland. As its designation implies, 

 the organism is small, and it is also attenuated. Its insect host is the tick 

 rhipicephalus appendiculatus, and it may be noted that this tick drops 

 off the animal on which it may be feeding when it is about to go through 

 one of its several moultings. It can thus carry an infection much more 

 quickly and widely through a herd than can the carrier of ordinary red- 

 water fever. It may be said that in England there occurs a red-water 

 fever also associated with the presence of a piroplasm in the blood, but 

 the relationship of this organism to the other varieties has not yet been 

 fully worked out. (3) Piroplasma equi. This organism gives rise to 

 biliary fever in horses, another South African disease, and it is carried 



