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 imsatisfactory. Recently, Mitzmain (1914) 

 has reported a series of experiments which show conclusively that the 

 disease may be so conveyed by a horse-fly, Tahanus 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 appHed two and one-half hovtrs, 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 tr3rpanosomiasis affecting especially horses and 

 mules, occurs in southern Asia, Malaysia, and the Philippines where 



