Abstract Several years ago at the autopsy of chicks which died with very few symptoms except poor growth, it was found that the lungs were either congested or filled with whitish nodules. Such nodules are usually considered diagnostic of infection with aspergillus. In this epidemic, aspergillus could not be found but instead numerous cocci were found which were identified as probably Micrococcu tetragenus. In one lot about 50 per cent of the chicks died while the rest were greatly retarded in growth. The source of infection was referred to the litter, although it was perfectly clean and good, since Micrococcus tetragenus is known to occur in such material. In later broods, sand replaced the litter and no further trouble was experienced with the exception of one lot of chicks were placed in a make-shift shelter on grass land beneath trees on the north side of a building. The grass was cut …