IXFLUKXCF. OF CLIMATE OX ANni \L DISFASE. 485 



\\'ith the winter months. Dnring the former time the warmth sO' 

 necessary for their development is sni)])he(l to them in greatest 

 degree, and hence the ticks increasing in activity and number, the 

 greater prevalence of tick-borne diseases is only to be ex])ected 

 granted that the stiital)]e vertebrate hosts are ijresent. We can 

 also understand how it is that ticks are generally more prevalent 

 in the warmer, low-lying l)nsh\eld and coastal belts than in the 

 middle and high veld areas, a distribution which, as Theiler 

 remarks. the South. Vfrican farmers recognised when they applied 

 to the tick the generic nauK' of Bos! ins. If we take a disease 

 such as redwater, transmitted b\- the blue tick, we can exjilain 

 why that, although cases of the disease are met with all the year 

 roitnd. they are more markedl\- i^revalent in the summer and 

 autttmn months, and we also can explain its greater general pve- 

 valence in low-lving. warm areas of the bush veld or coastal 

 regions, as in the Transvaal low veld, in Natal, and in the eastern,, 

 southern, and south-western portions of Ca])e Province, when 

 these areas are compared with the higher \'eld areas of the Trans- 

 vaal. Orange Free State. North-\\'cstern C^pe districts, and 

 Basutoland. It is recognised that other condition.s affecting the 

 distribution of the disease, such as trekking from high to low 

 veld pastures, will influence the spread of the disease, but these 

 considerations and others, such as the non-occtu-rence of the 

 ved-^\•ater in alleged susce])tible cattle when jjlaced in contact 

 with alleged infected cattle in the presence of the blue tick in 

 the Karroo region of Cape I'rovince, must be left over for 

 another time. 



Reference has already been made above to the brown tick in 

 considering the eft'ect of climate on its distribution and life- 

 history, and we might, if we wished, sho^^• how our knowledge of 

 the distribution and occurrence of East Coast fever fits in with 

 what we know of the habits of this and other ticks transmitting 

 the disease, but it does not seem necessary to do so here. Due 

 observation mav be mentioned, however, as, if correct, being still' 

 unexplained. It has been said that when the disease was gener- 

 ally prevalent in the Transvaal some years ago. it tended to dis- 

 appear very quickly from the high veld areas when introduced' 

 there. It was also pointed out that this could not be explained 

 as being due to the absence of the transmitting ticks, since, 

 although the brown tick is rare in this region, the red tick is also- 

 to be found there. Theiler does not believe that the cold condi- 

 tions of the high veld can be held directly responsible for this 

 occurrence, and one suggestion put forward was that it perhaps 

 depended on the fact that regulations restricting the disease were 

 more strictly complied with in the high veld, where the native 

 ]iopulation is smaller than in the low veld regions, and in which 

 latter places illicit movements of animals by natives was very 

 often practised. Further explanation is. however, necessary, but 

 it is interesting that Theiler showed, when experimenting in this 

 connection, that infected brown tick nympha;, ke])t for half an 

 horn- at 0°C. every dav for three weeks, were still infective in 



