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190 In the chronic form there is well-marked enlargement of the thyroid, with accompanying myxœdematous symptoms, as loss of hair, mental debility, etc. The lymphatic glands are always enlarged. In some instances there is marked bronzing of the skin, as in Addison's disease, depending on implication of the suprarenal capsules. In others, where the brunt of the infection has fallen on the heart, there is great irregularity in the action of this organ. In yet others aphasia, ataxia, spasm, athetosis, tremor, or other nervous symptoms indicate that brain, or spinal cord, or both have become implicated. Generally there is a combination of several of these conditions. Throughout, an irregular fever comes and goes, and there is always pronounced anæmia. The chronic form is that most commonly encountered in youths or adults; it is probably carried on from infancy or childhood, or kept up by reinfection.

The parasite.— During the febrile attacks the parasite (Fig. 51) in variable numbers is to be found in the blood, free or, rarely, partially included in red blood-corpuscles (Chagas). It averages about 20/u in length and has the usual trypanosome characters. The undulating membrane is narrow and the nucleus and blepharoplast are large. It is easily cultivated.

After ingestion by the insect intermediary the trypanosomes multiply in the gut. Some pass out with the faeces, which thus become infective if inoculated into a wound, or if applied to a mucous surface as the conjunctival sac (Brumpt). This, however, is not the normal way in which the infection is conveyed to man. In the midgut of the lamus, crithidia forms and, at a later stage, minute trypanosoma forms develop. It is the latter that, passing into the salivary glands, become the agents by which the infection is established. Eight days elapse after feeding on infected blood before the bug itself becomes infective.

Arrived in the human body the parasite multiplies, not in the blood (dividing forms are never found there), but in the cells of various organs,