_S. cruzi_ is found in the blood of children during the acute febrile stage but at other times in children, and as a rule in adults, it is rarely present in the peripheral blood. The early blood forms are narrow and very motile. They increase in size and slacken in motility when they become about 20 microns long. _S. cruzi_ is characterized by a very large blepharoplast. Dividing forms are never seen in the blood. The common site of multiplication is in the cells of the voluntary muscles and heart and also in the cells of the central nervous system, adrenals, and bone marrow. In these tissues the flagellate takes on a rounded form and undergoes binary division. Continued division converts the infected cell into a cyst. It is this process going on in various important structures that accounts for the extreme variation in symptomatology and pathology. Chagas thinks that the gametes for the cycle in _Lamus_ arise from parasites developing in the lungs of the vertebrate host. Flagellated parasites enter the lungs, lose the flagellum and become oval in shape, later on dividing into 8 parts. These assume an elongated form and enter the red cells of the host. Against this is the statement of various observers that the flagellates are only to be found free in the plasma, never within red cells. The forms taken up by _Lamus_ multiply in the intestine and then pass to the salivary glands after about 8 days. The bug is then infectious when it bites. Brumpt notes that infection may occur from inoculation of the faeces passed by the bug, especially through the conjunctiva. =Symptomatology.= _Acute types._—This form of the disease usually occurs in children under one year of age. The period of incubation is about ten days. It is attended by a high continued fever which may show a slight morning drop. There is marked puffiness of the face and enlargement of the thyroid. The lymphatic glands and spleen are also enlarged. The case may give the picture of a meningitis in which form the disease is exceedingly fatal. During the febrile period parasites are to be found in the blood but in the afebrile intervals which alternate with the febrile ones parasites are not present. _Chronic Types._—The type of the disease as seen in adults is mainly chronic. They often show enlargement of the thyroid and manifestations of myxoedema. The lymphatic glands are enlarged. Where the adrenal is attacked we have the syndrome of Addison’s disease. In the cardiac types there are present various forms of cardiac irregularities. In the cerebral types various neurological manifestations may be noted. An irregular fever may accompany the signs of involvement of the various important organs. The disease is attended by a marked anaemia.