4(So INFLUENCE OF CLIMATE ON ANIMAL DiSEASE. 



wet season. He also specially refers to i)aiis and edges of vleis 

 in Griqualand West as being repognised hotbeds of the disease. 

 In the Orange Free State it is also, according to information 

 received from the \^eterinary Department there, a disease of the 

 wet season, and it is said to have been usually. ])revalent there 

 during this year. 



Again the connection between rainfall and the spread of the 

 disease can be brought out in the unusual prevalence of the dis- 

 ease on the VVitwatersrand area of the Transvaal during the 

 early part of this year, the rainfall at this time being unusually 

 heavy. 



All of these facts, then, seem to point to the great importance 

 of water in the spread of the disease in South Africa, and it 

 may be stated as the opinion of the V^eterinary Research Divi- 

 sion that collections of water, such as i^ans, etc., from which 

 animals are watered, very probably play a large part in the dis- 

 semination of the disease in this country, these collections of 

 water being probably infected through the rain washing into 

 them anthrax spores derived from soil infected in the way 

 already indicated. That water may possibly also be important 

 in spreading the disease in another way in this country is shown 

 by Theiler's remarks in writing about the outbreak of anthrax 

 amongst ostriches in the Oudtshoorn district, in which case he 

 thinks that the water used for irrigation purposes must be held 

 largely responsible for the spread of the disease in that ])lace. 



These, then, are just a few of the ])oints we meet with in 

 studying the effect of climatic and local conditions on the spread 

 of one disease of the bacterial group. Black-quarter is another 

 disease with a very interesting distribution and occurrence we 

 might have dealt with, and two other diseases connected with soil, 

 such as malignant (Txlema and tetanus, we might also have 

 briefly referred to if we were not forced through consideration 

 of time to dro]) our considerations of the bacterial diseases at 

 this point. 



Let us remark, however, in passing, that in regard to the 

 actual conditions of life in the soil of disease-producing organ- 

 isms little is really known, although our knowledge of their 

 behaviour in the animal body and in culture media is extensive. 

 It is only within the last few years that the importance of the 

 protozoa of the soil as agents influencing the prevalence and acti- 

 vity of soil bacteria has been brought into prominence through 

 the researches instituted by Russell and Hutchinson. This im- 

 portance is one which, owing to the recent nature of the study, 

 has not yet been grasped in all its details, but it is to be expected 

 that in the future the work of those who specialise in the study 

 of soil biology will throw much light on the life-history of those 

 bacteria in which we are particularly interested. 



Leaving, then the bacterial diseases, we proceed to the 

 second group, taking first into consideration the diseases carried 

 bv ticks. 



