TO SOME DISEASES OF STOCK 
38B 
But of all natural orders commend us to the Arthropoda, 
a phylum containing jointed-limbed species of such diversity 
as Crustacea , represented here by the crayfish and prawn, which 
sometimes graces the Nairobi epicure’s table : as Insecta, with 
its orders Diptera or flies, into which fall, in addition to the 
common fly, the mosquito and the tsetse : Syphonoptera or 
fleas, Hemiptera or bugs, and Anoplura or lice — in all of which 
the housewife of Nairobi, the man in the trenches, and even 
the Medical Officer of Health join issue in wondering why 
they should not possess a more interesting relationship to their 
second cousin the lobster than that afforded by natural history 
alone. 
To the third great class of the Arthropoda, known as 
Arachnida, belong not only the two first cousins — the mites 
of cheese and the parasites of mange and scab — but also the 
family of Ixodidae or ticks, concerning which more hot air has 
filtered over East Africa than over the Sahara, and which has 
provided more grounds for thoughts and thoughtlessness, 
more excuse for the exhaustion of the limited supply of 
stationery than would be worthy of the largest animals — 
elephants, ichthyosauri, or even the modern tank. 
The subject of the present paper deals largely with this 
family of Arthropoda, whose members are the carriers or the 
hosts of the diseases we shall discuss ; but let it be understood 
at once they are not themselves the causes. We speak of 
tick fever, of sand-fly fever, of tsetse-fly disease : yet, strictly, 
these terms are wrong. Many ticks and all tsetse-flies are 
born clean and harmless to both man and beast : it is only after 
it has acquired infection by feeding upon a being which is or 
may have been sick that the real causal entity becomes acquired, 
and under certain defined conditions becomes elaborated to 
such a state that a succeeding bite by fly or tick will give the 
disease to the new animal. 
In some cases the fly is merely a mechanical carrier or 
vector of the noxious disease-producing factor — as, for example, 
the common house -Ay, Musca domestica, in its relation to typhoid 
and cholera of man ; but, with certain exceptions, the conditions 
we shall discuss here are those in which the fly and the 
tick play a real live part in the multiplication of the causal 
