Trypanosoma cruzi is easily cultivated in tissue cultures of chick embryos, but it was not possible to infect chicks with trypanosomes cultivated for more than 2 years in chicken cells.The trypanosome cycle takes place in one cell unit.The number of trypanosomes formed in one cycle depends on the volume of the host cell.The transformation of the leishmania form into the flagellate form begins when the cell is full of parasites, and occurs in 12–24 hr.The intracellular trypanosome, immediately after the crithidia form, is broad and short, the thin form probably being a later phase of the evolution of the parasite.Division of the adult trypanosome, or mating between the thin and broad forms, was never seen.At the beginning of the infection the cells with-stand the parasites and continue to proliferate, but finally they are destroyed.