FLIES AS CARRIERS OF DISEASE 47 



somes of horse and cattle diseases from one animal to 

 another, as do the species of Glossina or tsetse-fly. 



But we have yet to learn more about these flies and 

 the parasites they transfer. In the case of the gnat, it 

 has been discovered that the malaria parasite is swal- 

 lowed by the gnat, and multiplies in it, producing 

 thousands of spores in its blood, and it is these spores 

 which the gnat hands or rather " mouths " on to man. 

 No such multiplication of the trypanosome in the tsetse- 

 fly (Glossina) is known. The tsetse-fly passes on the 

 trypanosome as it received it, and yet it seems as 

 though it is not any and every biting fly which can pass 

 on the trypanosome of nagana, or of sleeping sickness, 

 but only the particular species of tsetse-fly. Perhaps 

 it is a case of greater abundance, the tsetse-flies being 

 the obvious and dangerous carriers of trypanosome 

 disease where they occur, on account of their abundance 

 and the fierceness and celerity of their attack. It is 

 almost certain that in India, Burma, and South America 

 some other flies must transfer the trypanosomes from 

 animal to animal, causing the diseases known as surra 

 and mal de caderas, because no tsetse-flies that is to 

 say, no flies of the genus Glossina occur in those 

 countries, and no other mode of transference, except by 

 some blood-sucking insect, seems probable. 



Ants in Africa are carriers of infection, and possibly 

 also in London kitchens, where a little red ant some- 

 times abounds. The black beetle or cockroach is a 

 creature to be got rid of, as it is very probable that it 

 spreads certain kinds of infection over food and dishes 

 during the hours of " revelry by night " which kind- 

 hearted people allow it to enjoy in their kitchens. 



