236 SECTIONAL ADDRESSES, 



Onderstepoort Laboratory had produced nothing else except this method 

 of immunising mules, its existence would have been justified. 



In horses the method has not been quite so satisfactory. A method of 

 immunisation of horses which would be safer, simpler, cheaper and more 

 reliable than the present method, would be of inestimable value to stock 

 farmers right throughout Africa. Recent work at Onderstepoort with a 

 formalised vaccine (by Du Toit and Alexander), seems to justify the hope 

 that such a method will be found. The work was inspired by the brilliant 

 researches of Dunkin and Laidlaw in England on another virus disease, 

 Distemper of dogs. 



The second important virus disease of South Africa is Bluetongue of 

 sheep. The disease is of great economic importance and would have been 

 a very serious hindrance to the sheep farmer had it not been for the fact 

 that Theiler discovered a simple method of vaccination by means of which 

 the losses from the disease can be reduced to a negligible quantity. Every 

 year two to three million doses of this vaccine are issued to the farmers, 

 and the ultimate saving to the country must be enormous. 



Another African disease, ' Heartwater ' of cattle, sheep and goats, 

 should be mentioned here. Formerly this disease was classified as a virus 

 disease, but a few years ago Cowdry, working at Onderstepoort, found that 

 it was caused by a Rickettsia. It is possible that this discovery may give 

 us a clue to a successful method of combating this serious disease. In the 

 meantime, all that can be done is to dip the animals to eradicate the tick 

 which transmits the disease. 



Of the many other virus diseases of animals only one more need be 

 referred to here, namely Rabies. This most dreaded of all human and 

 animal diseases has been eradicated from many countries, and is being 

 kept out by strict quarantine measures. In 1918 the disease was intro- 

 duced into England with a dog which had been smuggled in in an aeroplane. 

 Strict measures were put into force and in a comparatively short space of 

 time the disease was stamped out completely. Methods of preventive 

 inoculation of dogs in countries where the eradication of the disease is very 

 difficult, have been tried on a large scale. The results have, on the whole, 

 been very good, but it is too early to predict the future scope of these 

 methods. 



Before leaving this group, it is necessary to point out that virus 

 diseases are not confined to our domestic animals, but are encountered in 

 human beings, on the one hand, and in the lower animals (e.g. insects) and 

 in plants, on the other. Co-operation between medical men, veterinarians 

 and plant pathologists, therefore, becomes imperative. The subject is 

 claiming the attention of many scientific workers and great developments 

 may confidently be expected in the future. 



4. Bacterial Diseases. 



Of the host of bacterial diseases only a few need be mentioned here. 



The deadly glanders which was known before the time of Christ and 

 which, 25 years ago, still caused severe losses amongst horses, and con- 

 stantly threatened the human population, has now been practically 

 eradicated from all civilised countries, thanks to the accuracy of the 

 diagnostic tests which are used to identify the disease. 



