ANIMAL INDUSTRY 447 



tests on the common species to ascertain their abihty to transmit 

 the disease. Early work in South Africa, especially that by Walkins 

 and Pitchford in 1906 suggested that regularly dipped animals 

 are protected, either against tick bite or against infection with the 

 protozoan parasites, by a concentration of arsenic in the superficial 

 layers of the skin. Observations made at Kabete have shown that 

 this is not the case, but that the effect of dipping is the obvious 

 one: ticks arc collected by cattle and carried to the dipping tank 

 for immersion; a proportion of the ticks survive to finish their feed 

 and even to deposit eggs, but the number and viability of the eggs 

 laid are considerably reduced (Cowdry and Ham 1932, Cowdry 

 and Danks 1933, Kenya 1930, D.R.). In this way the numbers 

 of ticks are reduced to a point at which it becomes extremely 

 unlikely that an infected animal will transfer its infection to 

 a suflficient number of clean ticks for the disease to be carried 

 on. It is evident that a certain density of stock is necessary for 

 the rapid cleansing of pastures, and that fencing is complementary 

 to the dipping. It has been demonstrated at Kabete and on a 

 number of farms that susceptible herds of cattle can be maintained 

 in health in the centre of highly enzootic east coast fever areas, 

 but in the preliminary cleansing of pastures it is highly advan- 

 tageous to stock with immune animals. It is clear that research 

 on east coast fever and kindred diseases has now reached the stage 

 when any area of land can be rendered free of ticks, and the veteri- 

 nary authorities in Kenya and elsewhere are constantly urging in- 

 tensive campaigns for this purpose. 



A diagnostic test for pleuro-pneumonia, devised originally in Ger- 

 many and later standardized by Walker in Kenya, was in its day 

 most useful in assisting to clear up certain of the native reserves 

 and settled areas. The development of culture vaccine against this 

 disease was another outstanding feature of control, and between 

 130,000 and 400,000 doses of this vaccine are now issued from 

 Kabete free each year. There are now extensive areas free from 

 contagious bovine pleuro-pneumonia, and steps are being taken to 

 eradicate the disease from the remaining enzootic areas (Walker 

 1929b, Kenya 1935, Z).i?., Pt. II, p. 147). Meanwhile it is proposed 

 to carry out a complete reinvestigation of the etiology of the disease. 



The study of trypanosomiasis of domestic animals is in large part 



