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THE INCUBATION PERIOD OF THE EGGS OF 
HAEMATOPINUS AS INI. 
By A. BACOT, 
Entomologist, Lister Institute of Preventive Medicine, 
and L. LINZELL, 
Hon. Lieut., RA.V.C., Parasitologist, Central Veterinary Research Laboratory, 
R.A.V.C. 
INTRODUCTION. 
Three kinds of lice are found on horses, two belonging to the Mallophaga 
or scale-eating lice and one to the Siphunculata or blood-sucking lice. 
Of these, one, Trichodectes equi, is not very commonly found; whilst the 
other two, T. pilosus and Haematopinus asini, have both been common on 
the horses and mules of the Home Forces during the war. T. pilosus was 
found in about 10 per cent, of the total cases, usually as a mixed infestation, 
and chiefly in remounts from America or other places abroad, where the 
transport entailed a long sea voyage. 
Of the two latter kinds H. asini is the more important because: 
(a) It occurs more frequently.. 
(b) The irritation produced by it is greater. 
(c) Constitutional disturbances are set up in grossly infested cases to 
such an extent that a loss of condition progressing eventually to absolute 
emaciation is produced. 
(d) The possibility exists of this insect acting, like so many other 
blood-sucking parasites, as a carrier of disease, although hitherto no disease 
of horses has been definitely traced to it. 
(e) Lastly, it offers far greater obstacles to lasting eradication than 
do either T. equi or T. pilosus, and one of the most annoying features of 
infestation by this parasite is the tendency of apparently cured animals to 
become reinfested after the lapse of a few weeks. 
In view of the foregoing considerations, experiments were conducted 
only on the eggs of H. asini, and the following remarks apply only to 
that species. 
