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X] including the striped muscular fibres, especially of the heart, back, and lower extremities; also in the bone marrow, the thyroid gland, suprarenal capsules, nerve fibres and cells, testes, connective tissue, and other organs. Arrived in these it assumes a leishmania form (Fig. 56), divides and subdivides, distending the including cell till this becomes a mere cyst in which the parasites revert to the trypanosoma form. The cyst then bursts and the trypanosomes escape into the tissues, ultimately finding their way into the blood concurrently with an attack of fever. This is the form of schizogony by which the infection is kept up in the individual.

According to Chagas the gamete providing for the exogenous cycle in the insect arises from certain trypanosomes which, lodging in the lungs, lose their flagella and, approximating their extremities, form a ring, and then a sphere in which the nucleus divides, giving rise to eight daughter spheres. These elongate and, escaping, enter the red blood-corpuscles and become male and female trypanosomes, thus providing for the exogenous cycle in the insect (Fig. 51).

In the insect the parasite is not transmitted hereditarily, but the nymph, as well as the mature lamus, is capable of harbouring and transmitting the parasite. In the endemic districts all the bugs and many domestic animals are infected. Chagas considers that the armadillo, whose burrows are haunts of lamus, is the normal host of the parasite and a principal reservoir for the infection.*

Pathological anatomy.—— Inflammatory and consequent degenerative changes, the result of the presence of the parasite, are in evidence in most of the affected organs. Under the microscope the cyst like distended cells containing the parasite are to be found, particularly in the striated muscular fibres, and especially in those of the heart. The thyroid is enlarged, often sclerosed, with cystic cavities containing colloid material. The lymphatic glands and the spleen are also enlarged, the liver is fatty, serous