142 Journal op the Department op Agriculture. 



the separation of the colouring matter from the corpuscles, which is 

 deposited in the liver, and there undergoes a change into bile stain. 

 An over-production of bile takes place, which is carried into the 

 blood stream and absorption into the tissue follows. Hence we 

 recognize biliary fever in the horse principally by the yellow dis- 

 coloration of the mucous membranes. It is very rarely that the 

 destruction of the red corpuscles leads to colouring of the blood plasma 

 and to subsequent red urine. In the mule and in the donkey tiie 

 jaundice is not pronounced, and the white membranes indicating 

 anaemia are typical of the disease. 



The remarkable fact has been established that an animal, say a 

 horse, which has recovered from this disease retains the infection in 

 its blood. We cannot see the organism microscopically in the blood 

 of such an animal. The corpuscles have an absolutely nonnal aspect 

 and the animal to all appearances is healthy, but when we inject its 

 blood into a susceptible imported horse, mule, or donkey, we promptly 

 produce the diseavse, which can end fatally and be of such a virulent 

 character that it differs in no way from that contracted naturally. This 

 fact has been made use of to prove that tlie various piroplasms of the 

 horse and the donkey and of the hybrids are identical. 



In our experiments we have proved that the blood of an animal 

 which has recovered, and which for eighteen months has been kept in 

 a stable, still proved to be infective; and it can be concluded that 

 once an animal has recovered its blood remains infective for the 

 remainder of its life, ,at least if such an animal remains exposed in 

 the veld. 



This disease is carried by ticks, the ticks being the real hosis of 

 the parasites. Our experiments show that the common blue tick 

 (Boophilus decoloratus) is not implicated in the propagation of the 

 disease, but that the red tick (RJiipicephalus evertsi) acts as a trans- 

 mitter. 



We have transmitted the disease with ticks which have been 

 feeding on sick animals and on animals which had recovered. The 

 incubation time of the disease, when contracted from ticks, averages 

 abmit three weeks. 



Red WATER IN Cattle. 



South African redwater is due to the j/resence of Babesia 

 higemina (formerly called PrroplasTna higentimun), a parasite similar 

 to that of the horse, which invades the red corpuscles, multiplies and 

 increases in numbers, and causes the destruction of the corpuscles. 

 Whereas in biliary fever of the horse discoloured urine, due to the 

 breaking down of the red corpuscles, but rarely occurs, it is almost 

 an invariable symptom of redwater in cattle. 



As regards susceptibility, the conditions are similar to those 

 referred to above under biliary fever in horses. Cattle born and bred 

 on redwater-infected veld become immune. Tlie animals bred in 

 stables and imported from areas free of redwater contract the disease 

 easily and in many cases die. The calf is susceptible, but it usually 

 contracts the disease in a mild form and recovers comparatively 

 easily. It is then immune. Only under special conditions are break- 

 downs of immunity noticed. 



American investigators were the first to prove in a convincing 

 way that Texas fever, i.e. redwater, is a tick-transmitted disease, 



