HEMOFLAGELLATA, a soup of flagel lata Protozoa parastic in the blood of ver tebrates. The majority of these forms belong to the Try panosomatidce, or trypanosomes, which have come to be recognized as among the most serious disease-producing Evans in 1880 found them in horses in India afflicted with surra; Bruce in 1894 discovered another species to be the cause of nagafia in South African cattle and horses, and finally in 1898 Nepveu identified one in human blood. Rediscovered in 1901 in a European afflicted with intermittent fever, Dutton named it Trypanosoma gambiense, and a year later Cas tellani demonstrated its occurrence in sleeping sickness with which its causal relation has been abundantly demonstrated since then.
The Trypanosoma is spindle-shaped, with one (in other species rarely two) terminal flagella and a lateral, undulating membrane, the thickened margin of which is continuous with the flagellum. The nucleus usually lies near the centre of the body; a smaller body, known as the kinetonucleus or blepharoplast lies at the root of the flagellum near the anterior end of the organism. The complex life cycle has only been partially elucidated; it involves alter nation of hosts and probably also Transfer from one host to another is effected by a bloodsucking invertebrate, usually a fly. In the common species this is a Glossina or tsetse fly, in which certain stages of the life history are completed. While generally dis
persed by the circulatory system when intro duced into the vertebrate host by the bite of the fly, these parasites are more abundant in the spleen, bone marrow and kidneys, in the capillaries of which multiplication proceeds most rapidly.
The effects on the vertebrate host are vari able. In the natural or true host has been developed a tolerance that shows itself in the small number of trypanosomes present and in the absence of serious effects. On the other hand, in casual hosts which are not adapted to their attacks, serious effects follow the intro duction of trypanosomes. In man and the domestic animals introduced into new regions they evoke destructive epidemics such as have carried off cattle in Africa, or horses and mules in the Philippines. The wide spread and ter rible ravages of sleeping sickness in man in central Africa is a conspicuous illustration of the same phenomenon. In each case some native animal in which the parasite is unknown or unnoticed serves as the reservoir of the disease, from which it is transmitted to the new host by the attacks of biting flies also native to the region.