INSECT ENEMIES OF LIVE STOCK 191 



millimetres long in the female, and half the size in the 

 male. Its body is pitted in rows and irregularly. In 1903 

 Marchoux and Salimbini, in Brazil, discovered that the 

 tick, by its bite, transmitted a blood parasite, Spirochceta 

 gallinarum, to poultry. These spirochsetes, like the 

 organisms causing human tick fever, are spiral, thread- 

 like structures which swim about rapidly in the blood ; so 

 rapidly, in fact, that it is difficult to observe them. To 

 geese they are especially fatal, and hardly less so to ducks 

 and guinea-fowls ; doves and sparrows are less susceptible, 

 and in pigeons, after they have been bitten by an infected 

 tick, there is no illness, and no spirochaetes can be found 

 in the blood. The incubation period is usually four to 

 nine days, and it has been shown that an infective tick 

 can remain so for five months after its last infective meal. 

 Ornitkodorus moubata, the vector of human relapsing 

 fever, can also transmit spirochsetosis in poultry. The 

 disease is characterised by diarrhoea, anaemia, pallor of 

 the comb, and such weakness that the infected fowl lies 

 with its head on the ground. 



The eggs are laid in the hiding places of the ticks, 

 usually some crevice in the fowl house, and in three weeks 

 the six-legged larva hatches, and at once attaches to a 

 host for the purpose of feeding, and, at the next moult, 

 attains the flattened form typical of the adult, and so well 

 adapted for hiding in narrow cracks, beneath boards, etc. 



THE HEN FLEA 



The hen flea, Sarcopsylla gallinacea (fig. 54), is very 

 much smaller than the human flea, and of a reddish-brown 

 colour. Discovered in Ceylon, it has since been encountered 

 in Turke tan, German East Africa, Cameroons, Cape of 

 Good Hope, Italy, Madagascar, and the Southern States of 

 America. Though its usual hosts are chickens and ducks, 

 it has been known to attack horses, rats, and children. Its 



