396 



Texas-fever or Red-water in Cattle, [aug., 



alone, but importation is almost prohibited when they have 

 to be maintained and fed perpetually in separate stables, or 

 exposed to the risk of a loss of from 50 to 90 per cent, conse- 

 quent on putting them on the pastures with indigenous cattle. 

 It is too soon to report definitely on the results of the exposure 

 tests on the African pastures, as the experimental exporta- 

 tions are still going on, but it is probable that if these trials 

 turn out successfully, one of the results will be an increased 

 export trade in pedigree cattle. 



In consequence of the presence of these and other cattle at 

 the laboratory, it was possible to carry out an investigation 

 into Red-water in England. 



Earlier Investigations into Texas-fever. — In 1888 Smith 

 and Kilbourne, working in America, showed that Texas-fever 

 was due to small parasites (haematozoa) invading the red cells 

 of the blood, and in 1893 the same authors demonstrated that 

 the blood of animals sick or recovered from the disease would 

 cause Texas-fever in healthy animals if inoculated. It was 

 known that sick animals did not infect healthy ones by mere 

 cohabitation, and it was proved by Smith and Kilbourne that 

 female ticks which had sucked on affected or recovered cattle 

 produced a progeny of young ticks which conveyed the 

 disease. The length of time during which the blood of re- 

 covered animals remains infective, and therefore capable of 

 infecting ticks, varies considerably, but in the case of tropical 

 piroplasmosis, it may remain potentially infective for several 

 years. 



Similarity between Texas-fever and Red-water, — Since 1901 

 it has been known, as the result of an observation made by 

 the late Prof. Nocard, that parasites, morphologically inden- 

 tical with those found in connection with Texas-fever, may be 

 found in the red blood corpuscles of animals suffering from 

 the disease known as Red- water in Great Britain. Working 

 in collaboration with Sir John Macfadyean, Mr. Stockman 

 has shown, as the result of experiments performed at the 

 Board's laboratory, that the blood of animals suffering or 

 recovered from English Red-water is capable of infecting 

 other susceptible cattle with the disease after an incubation 

 period of from six to ten days. 



It has been established that Red-water in England coin- 



