PAEASITES 421 



condition by the tick having four pairs of legs instead of 

 three. Once more the tick, now much larger, finds an 

 animal host, again gets distended with blood, drops off on 

 to the ground once more, and for the second time goes 

 through the process of moulting and a change of appen- 

 dages. From this is finally produced the adult tick, 

 which finds its way on to an animal by grass or bushes, 

 as previously described, drops off when full of blood, and 

 the female ends its life by laying several thousands of 

 small eggs, which again go through the stages of larva, 

 nymph, and adult. 



The rate of development of these changes depends on 

 the temperature. They are retarded by cold and accelerated 

 by heat, but at most not more than two generations are 

 produced in one year.* 



The blue tick of Texas Fever can only renew its infection 

 through diseased or immune cattle, so that should it pass 

 its life on the horse, sheep or goat, the infection in the next 

 generation is entirely lost. 



In malignant jaundice of the dog the infected larva may 

 be carried by a jackal, the nymph carried by a cat, and 

 finally the adult give a dog the disease though no strange 

 dog has been in the place for years. In the same way the 

 infected brown tick of East Coast Fever may be carried 

 by many hosts and finally infect cattle ; the Heart-Water 

 tick if infected may pass its nymph stage on the horse, be 

 carried some distance, and should it pass its next stage on 

 a susceptible animal Heart-Water results. It will be seen 

 that the great danger with these ticks results from the 

 various dropping stages, for they retain their infection in 



* All that is here related about ticks and their life-history is taken 

 from the published papers of Mr. C. P. Lounsbury, B.Sc, Government 

 Entomologist, Cape Colony, who has devoted years of work to the 

 question of ticks in connection with animal diseases, and has recently 

 discovered the remarkable part played by the tick of East Coast Fever 

 in transmitting this plague. See particularly Agriculiural Journal 

 Cape of Good Hope, vol. xxiv., No. 4, 1904. Compare also Theiler, 

 ' Transmission of East Coast Fever by Ticks,' the Transvaal Agricul- 

 tural Journal, vol. iii., No. 9, 1904. 



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