_In the chronic form_ Chagas reports several varieties: (_a_) A pseudo-myxœdematous form, occurring in most cases, especially up to the age of 15. There is hypertrophy of the thyroid gland or at least signs of hypothyroidism, general hypertrophy of glands, disturbance of heart rhythm, and nervous symptoms. (_b_) The myxœdematous form is characterized by similar symptoms, especially by considerable swelling of the thyroid body, and myxœdema of the subcutaneous cellular tissue; sometimes there is a true pachydermic cachexia. (_c_) In the nervous form there are motor disturbances, aphasia, disturbances of intelligence or signs of infantilism, athetosis of the extremities and idiocy. There are also paralytic symptoms of bulbar origin, disturbances of mastication, phonation and deglutition, and in some cases convulsive attacks. (_d_) The cardiac form, characterized by disturbance of the heart rhythm. In all these forms the parasite is found at autopsy in the nervous substance, brain, bulb and heart. Vianna (1911)[89] has studied the histopathology of the disease. Some of the chief points are: in the heart muscle destruction of the sarcoplasm, followed by interstitial myocarditis; in the central nervous system invasion of the neuroglia cells and inflammatory reaction; in the suprarenal capsule invasion of medulla or cortex; inflammatory reaction can also be seen in the kidneys, the hypophysis and thyroid gland. [89] _Mem. Inst. Oswaldo Cruz_, iii, p. 276. Recently Chagas states[90] that “schizotrypanosomiasis” has been found in a child 15 to 20 days old, and that _Trypanosoma cruzi_ has also been found in a fœtus--the mother being infected with the trypanosome. The trypanosomiasis can, then, be transmitted hereditarily. [90] _Rev. Med. S. Paulo_ (1912), xv, p. 337. *Trypanosoma lewisi*, Kent, 1881. The trypanosome has a nucleus somewhat displaced anteriorly, about one-third of the way from the anterior (flagellar) end of the body, a relatively straight edge to the undulating membrane, and a rod-shaped blepharoplast (fig. 37, A). It averages about 25 µ long and 1·5 µ broad. Much attention has been devoted in recent years to the elucidation of the life history of the rat parasite, _Trypanosoma lewisi_. It is usually non-pathogenic to its host. It has been shown that the trypanosome can be transmitted from rat to rat by the rat-flea, _Ceratophyllus fasciatus_, and by _Ctenocephalus canis_ (the so-called dog-flea). (See also p. 92). The flagellate may also persist, but doubtfully develop, in the rat-louse, _Hæmatopinus spinulosus_. These researches may now be summarized.