TO SOME DISEASES OF STOCK 
895 
I have not enumerated the different species of Glossina 
occurring in this Protectorate, or attempted to describe the 
particular habits of life of each. As carriers or hosts of trypano- 
somes, they are all one ; though the severity of disease will 
be modified by habits, just as was the case with mechanical 
transmission by Stomoxys and Tabanus. A tsetse which 
prefers a desert and comparatively game-free country will 
naturally be less prone to infection than one which lives in a 
bush and densely game-packed district. The chief carrier of 
sleeping sickness is Gl. palpalis — a fly that will not live away 
from certain types of river banks. Such an insect must 
eventually be more dangerous to people who day by day have 
to go to the river for water or fishing, than one like Gl. morsitans, 
which will live many miles from water and has a wide range 
of flight. The odds against any one man coming in contact 
with the same fly at a future time are much less in the 
case of the restricted and somewhat domesticated palpalis 
than in the disseminated morsitans, which studiously avoids 
habitations. 
Let us now turn to the second class of Arthropoda, which 
we said sucked blood, and were of importance as disease 
producers — the Arachnidae. 
Of the five principal orders into which the Arachnidae 
are divided, and which include such forms as spiders and 
scorpions, only one, the Acarina, is relative to our present 
subject. 
The Acarina themselves are divided into a number of 
families, of which the Ixodidae, or ticks, and the Sarcoptidae, 
or mites and mange parasites, are the only ones of immediate 
interest. 
The diseases produced in animals by the Sarco'ptidae are 
in great measure comparable to those due to lice and fleas : 
they are, fundamentally, of an external and irritating character, 
and due to the mechanical annoyance of this parasite itself 
rather than to any specific micro-organism conveyed. Itch 
in man, mange in dog and horse, and scab in sheep, are the 
principal conditions : each is due to distinct and specific forms, 
which only exceptionally pass from one species of animal to 
another. Although known as mange in each case, there 
