M.— AGRICULTURE. 235 



The extent to which dipping is practised to-day may be gauged by the 

 fact that there were in the Union of South Africa in 1929 more than 

 13,500 dipping tanks. If we assume that the average dipping interval is 

 eight days (the actual intervals are three, five, seven or fourteen days), and 

 that the average number of animals that pass through a tank on a dipping 

 day is 200 (frequently the number is as high as 4,000), we find (calculating 

 on this very conservative basis) that about 120,000,000 cattle passed 

 through the dipping tanks last year. 



Returning now to the campaign against East Coast fever, it may be 

 said that by means of carefully controlled dipping and hand-dressing of 

 cattle, combined with quarantine restrictions, and slaughter of infected 

 herds in the case of isolated outbreaks, it has been possible to keep the 

 disease well under control. The hope seems justified that the disease will 

 be eradicated completely from South Africa and Rhodesia before many 

 years have passed. That this would be a great boon to the cattle industry 

 of these two countries needs no further emphasis. 



In the United States of America, where Texas fever (Redwater) is the 

 only serious tick-borne disease, an attempt is being made to eradicate the 

 transmitter, Boophilus annulatus, completely by means of dipping. Large 

 areas have already been cleared of these ticks, and the economic advantages 

 to which these areas are entitled after being declared tick free more than 

 compensate for the expenses incurred. 



3. Virus Diseases. 



The vast sums of money which have been spent in this country during 

 the last few years on the eradication of Foot and Mouth disease should 

 convince even the layman of the importance of this group of diseases. 



In the olden days it was Rinderpest which caused the severest losses. 

 It has been calculated that the losses in Europe during the eighteenth 

 century amounted to 200 million head of cattle. The disease made its 

 appearance in England in 1865. A Royal Commission was appointed and 

 its report is of value to this day. Later on, improved methods of 

 eradication and prevention were evolved, and to-day most countries are 

 free of Rinderpest. However, in the Far East and in Central Africa the 

 disease is still prevalent, and causes very serious losses. 



Two recent outbreaks of Rinderpest, one in Belgium in 1920, and the 

 other in Australia in 1923, both of which were eradicated completely 

 within a few months, have again shown how far Veterinary Science has 

 advanced during the last century and how much a country owes to an 

 efficient Veterinary Service. 



South Africa has been free of the two diseases just named for many 

 years. But there are several other virus diseases which play a very 

 important role. Among these ' Horsesickness ' and ' Bluetongue ' of sheep 

 are perhaps the most important. An extensive study of the former 

 di.sease by Theiler and his co-workers has yielded some very valuable 

 results, but the problem of Horsesickness cannot be said to be solved. At 

 present a method of immunisation with hyperimmune serum and virus 

 is practised, and this method has given excellent results in mules. About 

 4,000 mules are immunised annually, and it has been stated that if the 



