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Three series of experiments were conducted to investigate the refractoriness of chickens to Trypanosoma (Schizotrypanum) cruzi. Firstly, 60 newly hatched chicks were inoculated with either bloodstream trypomastigotes or triatomine faecal stages of T. cruzi. The chicks were kept at low ambient temperatures, then killed at intervals and examined for infection by direct microscopy of body fluids, xenodiagnosis and sub-inoculation of mice with peritoneal fluid, blood and organ suspensions. None of the chicks supported growth of T. cruzi. Secondly, 19 chicken embryos were inoculated with culture forms of T. cruzi. Nine embryos were then further incubated at 36.5 degrees C and ten at 41 degrees C. Six of the former group were found, by sub-inoculation of blood into culture media, to be infected but all of the latter group were uninfected. Finally, diffusion chambers, containing either culture or faecal triatomine stages of T. cruzi, were surgically implanted into the peritoneal cavity of three chickens and also into rats as controls. T. cruzi survived in the chicken diffusion chambers for up to three hours but not to 18 hours, whereas in the chambers in the control rats living T. cruzi organisms were found up to the end of the observation period of seven days. These results suggest that the insusceptibility of chickens is mainly due to humoral factors but that the high body temperature of 41 degrees C may also play some part.

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