TRANSACTIONS OF SECTION I. 553 
2. The Advance of our Knowledge respecting the Stock Diseases of 
South Africa. By Dr. A. THEILer. 
1, Diseases caused by ultra visible micro-organisms :— 
(a) Horse-sickness and malarial catarrhal fever may be considered together: 
both occur under similar telluric and climatic conditions, but the former is more 
especially prevalent in low-lying parts, while the latter is found on higher levels 
where, in epizootic years, the horse-sickness may also appear. Both diseases 
oceur during heavy rains, especially during the latter half of the rainy season. 
Animals are infected during the night. They cease as soon as frost comes. Both 
are inoculable in animals of the same species, but are not contagious. The two 
diseases, horse-sickness and Blaauw tongue or catarrhal fever, are distinct. The 
virus is easily destroyed by desiccation, but is not affected by cold. Both are 
conveyed from animal to animal by nocturnal insects. Veterinary Surgeon 
Spreuill, of the Cape Colonial Service, by hyper-immunising sheep with virulent 
blood has succeeded in producing a serum efficacious in cases of Blaauw tongue. 
The author has succeeded in immunising mules against horse-sickness by the 
simultaneous subcutaneous injection of serum and intravenous injection of virus. 
The resulting death-rate is 5 per cent. It is higher in horses. 
(6) Heart-water in sheep and other domestic ruminants.—This disease is 
inoculable from sick oxen to susceptible oxen, sheep, and goats. The organism is 
attached to the red blood-corpuscles: it cannot be cultivated, and does not pass 
the Berkefeld filter. Blood loses its virulence in forty-eight hours, Heart-water 
is not contagious. Mr. Lounsbury, of the Cape Service, found that it was pro- 
pagated by the Amblyomma hebreum, commonly known as the tortoise tick. 
Certain varieties of sheep suffer less than others; for instance, Persian sheep may 
sicken, but do not die. The tick may be eradicated by repeated dippings over a 
protracted period, but at present this is not practicable in the Transvaal. Animals 
hyper-immunised produce a powerful serum, 
2. Diseases caused by protozoa :— 
(a) Diseases caused by Piroplasmata. 
(6) Diseases caused by Trypanosomes. 
(c) Diseases caused by Spirilla. 
(a) There are two varieties of Piroplasma: of one, the Piroplasma bigemi- 
num of Texas fever may be considered as the type, and the Piroplasma parvum 
of Rhodesian fever as the type of the second. “To the first type belong the Piro- 
plasma equi and the Piroplasma canis. The diseases caused by these parasites 
are characterised by anemia, jaundice, hemoglobinuria, and an’ enlarged spleen, 
All three are inoculable and recovery results in a certain amount of immunity. 
They are all spread by ticks—Redwater by the Rhipicephalus decoloratus and the 
Rhipicephalus annulatus ; equine Piroplasmosis, or biliary fever of horses, is 
spread by the red tick, Rhipicephalus evertst; biliary fever, or malignant jaundice 
of dogs, is conveyed through the dog tick, Hemophysalis leachi. There is only 
one disease caused by organisms of the second type, Pirosoma parvum, and that 
is Rhodesian fever. It is not conveyed by inoculating a susceptible animal with 
the blood of one suffering from the disease. It is communicated by two ticks, the 
Rhipicephalus appendiculatus and Rhipicephalus simus, The infection does not 
pass through the egg, and an infected tick having once bitten cannot again cause 
the disease. The blood of the immunised ox does not contain the parasite in any 
shape ; consequently after a farm has been cleared of cattle for fourteen months it 
can again be stocked with safety. 
(0) Diseases caused by ‘'rypanosoma: (i) Nagana, or tsetse-fly disease ; 
(ii) Specific trypanosomasis of cattle. 
Nagana only exists in a few places in Zululand and Rhodesia. Dogs and 
horses are very susceptible, but sheep and goats have a prolonged disease, and the 
ox may survive for years. The disease is conveyed by the fly Glorsina morsitans. 
Specific trypanosomasis of cattle occurs all over South Africa, Infected cattle 
