Some Illustrations of Direct Inoculation 165 
Some Illustrations of Direct Inoculation of Disease Germs 
by Arthropods 
In discussing poisonous arthropods, we have already emphasized 
that species which are of themselves innocuous to man, may occasion¬ 
ally introduce bacteria by their bite or sting and thus cause more or 
less severe secondary symptoms. That such cases should occur, is 
no more than is to be expected. The mouth-parts or the sting of 
the insect are not sterile and the chances of their carrying pyogenic 
organisms are always present. 
More strictly falling in the category of transmission of disease 
germs by direct inoculation are the instances where the insect, or 
related form, feeds upon a diseased animal and passes promptly to a 
healthy individual which it infects. Of such a nature are the follow¬ 
ing: 
Various species of biting flies are factors in the dissemination of 
anthrax, an infectious and usually fatal disease of animals and, 
occasionally, of man. That the bacteria with which the blood of 
diseased animals teem shortly before death might be transmitted 
by such insects has long been contended, but the evidence in support 
of the view has been unsatisfactory. Recently, Mitzmain (1914) 
has reported a series of experiments which show conclusively that the 
disease may be so conveyed by a horse-fly, Tabanus striatus, and by 
the stable-fly, Stomoxys calcitrans. 
Mitzmain’s experiments were tried with an artificially infected 
guinea pig, which died of the disease upon the third day. The flies 
were applied two and one-half hours, to a few minutes, before the 
death of the animal. With both species the infection was success¬ 
fully transferred to healthy guinea pigs by the direct method, in 
which the flies were interrupted while feeding on the sick animal. 
The evidence at hand does not warrant the conclusion that insect 
transmission is the rule in the case of this disease. 
The nagana, or tsetse-fly disease of cattle is the most virulent 
disease of domestic animals in certain parts of Africa. It is caused 
by a protozoan blood parasite, Trypanosoma brucei, which is con¬ 
veyed to healthy animals by the bite of Glossina morsitans and possi¬ 
bly other species of tsetse-flies. The flies remain infective for 
forty-eight hours after feeding on a diseased animal. The insect 
also serves as an essential host of the parasite. 
Surra, a similar trypanosomiasis affecting especially horses and 
mules, occurs in southern Asia, Malaysia, and the Philippines where 
