Vital reactions to frostbite of the ear and paw skin in guinea pigs exposed to the cold.

Vital reactions to frostbite in the paw and ear skin of guinea pigs were studied in order to find an animal model for frostbite in cases of accidental hypothermia. One group of animals was rendered hypothermic (rectal temperature, 30 degrees C) by exposure to an ambient temperature of -20 degrees C, and samples were taken from the frozen skin. A second group was rendered hypothermic and rewarmed in warm air at 45 degrees C, and samples were taken from the thawed skin. The only vital reaction in the first group (freezing time, 4-5 h) was mild initial inflammation, which was expressed in granulocyte adhesion to the vessel wall and the migration of a few cells into the dermis. The inflammatory reaction was more distinct in the second group (freezing and thawing together 5-7 h), with a large number of granulocytes being present in the dermis. Oedema and hyperaemia were also present in the frostbitten tissue after thawing, but no signs of necrosis developed. The alkaline-phosphatase reaction demonstrated the presence of granulocytes more clearly than H & E or Masson trichrome staining. Vital reactions were more advanced in the ear skin. It is concluded that vital reactions are very scarce in cases of frostbite, even after several hours' exposure, unless the tissue is allowed to thaw.