434 YETEEINAEY HYGIENE 



In cold weather they lie near the skin. Their presence 

 causes considerable irritation, not only from their move- 

 ments but from the punctures they inflict on the body. 



The insect is about one-quarter of an inch in length and 

 of a brownish colour. As it lives on the surface of the 

 skin, it is not difficult to destroy by arsenical or other 

 ' dips.' 



Hippohosca equina, the Forest-fly (Fig. 185), is a winged 

 member of the same family, and is a pest in the New 

 Forest. The fly is about one-quarter of an inch long, of 

 a glossy brown colour. It has a yellow 

 head, and three pairs of strong legs, the 

 feet of which are arranged for clinging. 

 These flies are blood-suckers, and their 

 movements on the horse are curious ; they 

 run backwards, forwards, or in a sideling 

 crab-like fashion, and cause in this way 

 ^. ,„. „. the most intense irritation to animals un- 



Fig. ISo. — Hip 1 J.1 j-ii2 



poiosca equina ; used to their attacks. They are both diin- 



sire'' '"'*''™^ cult to catch and to hold, and require 

 considerable pressure to destroy. 



Deer are also affected by a forest-fly peculiar to them- 

 selves. 



Hippohosca rufipes has been shown by Theiler* to be the 

 means by which the trypanosome of South African ' gall 

 sickness ' is transmitted from animal to animal. 



The Lice affecting animals may broadly be divided into 

 two groups : 



Biting lice of the genus Trichodectes. 

 Sucking lice of the genus Hcematopinus. 



Each of these genera has representatives on the horse, 

 ox, sheep, goat, and dog, save that Hsematopinus is said 

 by Neumann not to attack sheep. 



The horse is affected by one kind of Hsematopinus and 

 two of Trichodectes. The ox harbours two species of Hsema- 

 * Journal of Comparative Pathology, vol. xvi., part iii., 1903. 



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