LATENCY OF AFRICAN COAST FEVER. 229 



repeated changes of clean pasture land, is made plain by reason 

 of the active disjunction of the Koch's bodies up till the month 

 of May, so that the larvre are all the time able' to obtain fresh 

 elements of infection. On this theory the periods between 

 changes of pasture have been too long, in view of the fact that 

 efficacious dipping was out of the question. 



The apparent success in the elimination of the disease about 

 July is explainable, for indications are not wanting that where 

 infections are conveyed in the winter months, July and August, 

 instead of the production of merozoites — endo-globular bodies 

 in the erythrocytes — the formation of Koch's granules takes 

 place probably from the schizont phase ; further, such animals 

 do not then show high febrile reactions, neither do they suc- 

 cumb, except in rare instances. Such animals remain over to 

 the next summer or autumn as reservoirs of infection, and in 

 these we have a latent or endemic form. 



I am not even satisfied that infected blood inoculations con- 

 ducted in July will not in the same way give rise to the formation 

 of Koch's granules, and that the extensive outbreaks in the 

 Victoria district in 1905, 1906 and 1907 were not the result of Dr. 

 Koch's late inoculations in 1904 — an explanation as to why 't 

 was that coast fever practically disappeared and has since re- 

 appeared in increased virulence. 



After the havoc in the early part of the last decade a few 

 remnants were left, and most of these could be considered to 

 be immune or salted, and it was from these that the Rhodesian 

 stock-owners established their herds until fortune began to smile 

 again, and they were a.h\e to make outside additions. 



Now it is pretty conclusively proved that these remnants do 

 not harbour the micro-parasite, neither can they, for some years 

 at any rate, be reinfected; on the other hand, the progeny of 

 salted parents are not all resistant, and can contract coast fever 

 — in fact, one-third such calves succumbed to it. 



The country was practically left without bulls, as they were 

 especially susceptible, so in a number of instances no calves 

 were forthcoming to keep infection alive, and the disease dis- 

 appeared. In other instances young stock were born before the 

 infected ticks had had time to die out, and coast fever was kept 

 going, but unnoticed, owing — (i) to the farmer setting no store to 

 the death of a calf or two, and not deeming the cause of death 

 worthy of investigation; (2) the mortality was low, possibly not 

 one in three; (3) the loss was not continuous, but seasonal, 

 occurring mostly in the wet season, when it could be easily 

 conjectured that the calf was smothered in mud (nearly all 

 cattle are kept in open kraals in this country) ; so it simmered on; 

 then four years ago new susceptible cattle were introduced into 

 the herds, and the disease is assuming graver proportions, be- 

 cause more bovine hosts have been inserted. 



My observations have led me to different conclusions to 

 those generally expressed by other authorities, but a close study 



