Zöology; a textbook for colleges and universities . en mosquitoes and malaria was established not onlyby the observation of the organisms in the blood, butalso by the experimental transmission of the disease. Itwas also shown experimentally that men could live andwork in the most malarious districts, and suffer no harm,provided they were protected from mosquitoes at localities where there is no Anopheles, malaria cannotbe acquired, though persons who have acquired it else-where may continue to suffer at intervals. Anophelesmay even be present, but unless it is infected by thePlasmodiu
Zöology; a textbook for colleges and universities . en mosquitoes and malaria was established not onlyby the observation of the organisms in the blood, butalso by the experimental transmission of the disease. Itwas also shown experimentally that men could live andwork in the most malarious districts, and suffer no harm,provided they were protected from mosquitoes at localities where there is no Anopheles, malaria cannotbe acquired, though persons who have acquired it else-where may continue to suffer at intervals. Anophelesmay even be present, but unless it is infected by thePlasmodium, no malaria results. Sleeping 7. The important African diseases due to trypano- andnagana somes are also carried by insects, but of a different family of Diptera or flies. In this case the alternate hosts are species of tsetse fly, of the genus Glossina. PROTOZOA AND DISEASE 205 These look somewhat like house flies, but are recognizedby the long, straight proboscis projecting in front of thehead, and by the way in which the wings are folded over. From drawing by Jo/in T. Scott FIG. 44. Tsetse fly (Glossina palpalis), female; X 5 diameters. From a speci-men collected in Southern Nigeria, Africa, by G. Garden, April 28, ioog. Thisfly is widely distributed over tropical Africa. It has a formidable proboscis, andsucks the blood of man and other animals. In so doing, it transmits a minuteprotozoan, called Trypanosoma gambiense, which produces in man and monkeysthe disease known as sleeping sickness. From this disease many thousands ofthe inhabitants of Africa have perished. Another related protozoan, Trypanosomabrucei, is carried by a different tsetse fly, Glossina morsitans, and produces in cattleand horses the highly fatal disease called nagana. Tsetse flies once existed inColorado, as is proved by fossils found at Florissant. They may well have trans-mitted the organisms causing disease, and thus been instrumental in extermi-nating some of the larger animals. • Thus we find
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