Recently Stephens and Blacklock (1913)[86] have shown that two trypanosomes, different morphologically, have been confused under the name _T. brucei_. One of these is polymorphic (_i.e._, it exhibits long and slender as well as short and stumpy forms) and came from Uganda, while the other is monomorphic and is the original Zululand strain described by Bruce from cattle suffering from “nagana.” Bruce (1914) considers that morphological change has occurred in _T. brucei_ in its passage through laboratory animals, and thus explains the diversity of views. The posterior nuclear forms described by Blacklock occurred in the Uganda strain of _T. brucei_. (See p. 95.) Similarly, a posterior nuclear form, _T. equi_, has been separated from _T. equiperdum_. (See p. 98.) [86] _Proc. Roy. Soc._, B, lxxxvi, p. 187. Again, Bruce and his colleagues on the Royal Society Commission investigating sleeping sickness in Nyasaland, have stated (April, 1913) that “evidence is accumulating that _T. rhodesiense_ and _T. brucei_ (Plimmer and Bradford) are identical.” The exact identity of trypanosomes showing posterior nuclei is, then, far from settled, although Laveran by cross immunity tests has declared that _T. brucei_ is distinct from _T. rhodesiense_. No one has yet seen posterior nuclei in _T. gambiense_. *Trypanosoma cruzi*, Chagas, 1909. Syn.: _Schizotrypanum cruzi_, Chagas, 1909. The trypanosome was discovered by Chagas[87] in the intestine of the bug, _Triatoma_ (_Conorhinus_) _megista_, in Brazil, and then in the blood of a small monkey bitten by the bug. A little later it was found in the blood of a child, aged two years, suffering from irregular fever, extreme anæmia and enlarged glands in the State of Minas Geraes, Brazil. Chagas found that he was able to infect many of the usual laboratory animals with the trypanosome, by allowing the bug to bite them. He was also able to culture the parasite on blood agar. [87] _Mem. Inst. Oswaldo Cruz._, i, p. 159. Chagas found the Reduviid bug, _Triatoma megista_, in the houses of the poorer inhabitants of the Brazilian mining State, and that it attacked the people, more especially the children, at night, biting the face. On this account the insect is called “barbeiro” by the inhabitants. The bite is somewhat painful. The disease has since been found in other parts of Brazil, _e.g._, Matta de São João in Bahia province, Goyaz, Matto Grosso and São Paulo provinces, as well as in Minas Geraes. _Morphology._--The trypanosome has a large blepharoplast or kinetic nucleus. It is stated to occur both free and in the red blood corpuscles in the peripheral blood. It is about 20 µ long, on an average.