Observation in Practice. ^The history of the importation of cattle 

 from various Texas fever countries into the Transvaal after the conclusion of 

 the late war gives us a demonstration of the immunity under the condition of 

 natural exposure. Importations from Madagascar numbered 10,000 oxen. 

 These oxen are immune to redwater, as experience and experimental proof 

 have shown. The general experience was that these animals did not contract 

 redwater, and ever since cattle were imported from that country this fact 

 is generally admitted. Contrary to this, an observation of mnie shows 

 that freshly imported Madagascar cattle can suffer from redwater. Eight 

 Madagascar oxen brought from Natal, where they had been running for 

 a short time, were brought to the laboratory and directly after arrival 

 two succumbed to acute redwater. 



Texas cattle were also imported to the number of 10,000. Speaking 

 generally, these cattle proved to be immune to the South African redwater, 

 but also here were exceptions to the general rule. Some cattle which 

 had been running in Natal were brought to the Transvaal to be 

 used in connection with the East Coast fever experiment, and four 

 died within eight days after arrival from acute redwater. They un- 

 doubtedly must have contracted the disease previous to departure. 

 From Queensland 500 head were imported. In this case the experience 

 amounts to experimental value. The 500 head were inoculated with the 

 blood of an immune South African ox, with the result that some of the 

 cattle, few in number, contracted acute redwater and died. 



Speaking from general observations, all cattle born and bred on the 

 veld of the Transvaal must have gone through an attack of redwater and, 

 therefore, must be immune. The immunity is a generally accepted fact. 

 Yet during this summer outbreaks of redwater in all parts of the country 

 were very numerous, and in many cases in cattle which were born and 

 bred on the farm, or had been there at least for some years. In some 

 instances the redwater took the form of a real epizootic. 



It must be stated here that the climatical condition of the current 

 year was exceptionally favourable for the breeding of ticks. 



Conclusion. — Observations in fractice prove that immunity against 

 redwater naturally acquired gives a great protection against 

 subsequent exposure, but it is by no means complete. The 

 breahdovMS may be either due to infection with a difjerent strain 

 or to the over infection by means of ticks. 

 Redwater noticed as Complication of Other Diseases. — When 

 East Coast fever was first observed, it was noticed that in sick animals in 

 conjunction with small piroplasms, the typical Piroplasma bigeminum was 

 found. When later the small piroplasms were recognised as a species of 

 their own — PiroplasmMparvum— the iactoi the simultaneous presence of both 

 piroplasms in redwater immune animals found its interpretation in accept- 

 ing that, under the influence of the acute East Coast fever, the Piroplasma 



