M.— AGRICULTURE. 239 



(Monnig and Le Roux) and in many other parts of the world (notably in 

 the United States of America) will yield practical results. 



One further fact must be emphasised here. The menace of worm 

 infection has become so great that no sheep farmer can hope to be 

 successful if he disregards the teaching of modern science. Overstocking 

 of farms must be prevented at all costs ; marshes must be drained or the 

 sheep kept away from them ; the sheep must be treated regularly 

 according to the best methods known. If these precautions are adopted, 

 the parasites can be kept in check and profitable sheep farming will 

 become possible ; if the advice is ignored, then the financial loss to the 

 farmer will be the smaller the sooner he gives up farming. 



The great value of hygienic methods in farming has been proved in the 

 case of Ascaris infection of pigs. Some years ago the pig breeding industry 

 was seriously threatened by this parasite ; whereas to-day, thanks to the 

 researches of Ransom and others, the infection can be eliminated com- 

 pletely. 



6. External Parasites. 



The two most important groups of ecto-parasites, the ticks and the 

 tsetse flies have already been referred to. 



A further very important group are the mites. These minute parasites 

 are responsible for the diseases known as scab or mange in animals, and 

 have caused untold losses. In the fight against these diseases, the 

 British Dominions have had very signal success. Australia and New 

 Zealand have eradicated sheep scab completely, Canada is practically 

 free of it, and in South Africa, where the presence of a large native popula- 

 tion owning a very inferior class of sheep has made the campaign 

 particularly difficult, the incidence of the disease has been reduced to 

 infinitesimal proportions, and complete eradication within a short time is 

 hoped for. 



Another very important ecto-parasite of sheep is the so-called Blowfly. 

 The trouble is caused by these flies depositing their eggs in the wool of 

 sheep, especially in the soiled and moist parts, and by the resulting maggots 

 causing serious damage to the wool and the sheep itself. The pest has 

 assumed alarming proportions in Australia and is becoming more and more 

 important in other countries, including South Africa. Determined efforts 

 are being made to combat the pest and valuable progress has been 

 achieved. In this research entomologists and veterinarians are working 

 hand in hand. 



7. Diseases due to Poisonous Plants. 



That certain plants are poisonous and may have fatal effects when 

 consumed by animals has probably been known for centuries. However, 

 it is only during recent years that plants have been studied which produce 

 diseases comparable with epizootic diseases. In this field of research 

 South African workers have been prominent. 



One of the most remarkable of these diseases is that known in South 

 Africa as ' Gousiekte ' (rapid disease) of sheep, which was studied some 

 years ago by Theiler, Du Toit and Mitchell. The cause of the disease was 

 shown to be the plant Vangueria pygmcea. The remarkable nature of this 

 disease may best be illustrated by the following incident : A farmer 



