238 SECTIONAL ADDRESSES. 



5. Internal Metazoan Parasites. 



The only group that need be mentioned in this brief survey are the 

 Worms. These parasites have become more and more important and to-day 

 they actually constitute the ' limiting factor ' in successful sheep farming 

 in many parts of the world. This subject forms a highly specialised 

 science of its own, the science of Helminthology ; in which many notable 

 successes have been achieved in recent years. It is almost unnecessary 

 to add that this subject demands the close co-operation of zoologists, 

 medical men and veterinarians. 



Amongst the Trematodes the LiverfluJces and Schistosomes of sheep and 

 cattle deserve special mention. The latter group is not of very great 

 economic importance, but is of great interest because of the close relation- 

 ship between the disease in animals and Schistosomiasis (Bilharzia disease) 

 in man. Le Roux of Onderstepoort has shown recently (1929) how the 

 campaign against the human disease can benefit from further study of the 

 animal disease. This is particularly true of the method of treatment with 

 tartar emetic and other modern drugs. 



Liverfluke disease of sheep and cattle is a very serious problem in many 

 countries in different parts of the world. In Germany, Noller has 

 organised what may be termed a national campaign against these parasites, 

 and has achieved a large measure of success. Various preparations have 

 proved to be very efficacious in the treatment of infected am'mals, and the 

 application of modern principles of hygiene has reduced the incidence of 

 the snails which act as intermediate host of both groups of worms just 

 mentioned. 



Generally speaking, the Nematodes or round worms are far more serious 

 than either the Trematodes or Cestodes (tape worms). In many countries 

 where sheep farming is conducted on an extensive scale, the infection with 

 various nematode worms seriously threatens the industry. One or two 

 examples may be mentioned. 



The ordinary stomach worm of sheep {Hcemonchus contortus) is world- 

 wide in its distribution and is the cause of very severe losses. Better 

 farming methods will undoubtedly improve the position, but in the 

 meantime farmers look to the veterinarian to rid their sheep of these deadly 

 parasites. Various chemicals have been tried with varying degrees of 

 success, but perhaps nowhere has the success been so marked as in South 

 Africa, where, as a result of the researches of Theiler, Veglia, Green and 

 others, a method of treatment was recommended which has proved the 

 salvation of many sheep farmers. The method consists of the accurate 

 dosage of a mixture of arsenite of soda and copper sulphate ; and the 

 extent to which this method has been applied may be gauged from the 

 fact that at present some 25 million doses of the mixture are issued annually 

 from Onderstepoort. The method is not perfect, but it has certainly been 

 a great factor in making sheep farming a success where otherwise it would 

 have been a dismal failure. 



There are many other nematodes which threaten the sheep industry. 

 CEsophagostomum columbianum and various species of Trichostrotigylus are 

 amongst the most important in South Africa. Treatment in these cases 

 is not simple, but it is hoped that the work now proceeding at Onderstepoort 



