Effects of hyperthermia on the myelograms of adult and fetal guinea‐pigs

Summary. The myelograms of adult guinea‐pigs at various stages after brief exposure to hyperthermia were compared with those of control animals. The proportions of neutrophil and eosinophil metamyelocytes and of intermediate normoblasts were significantly reduced for at least 24 h after exposure and the proportions of neutrophil polymorphs and lobulated eosinophils were significantly increased over this period. The mitotic index was reduced for up to 5 h. Morphological changes in cells included hypersegmentation of nuclei, pyknosis, necrobiotic changes, development of pseudopodia, and abnormalities of mitosis. The myelograms of newborn guinea‐pigs which had been heated on days 20–23 of pregnancy showed no significant changes.