Ultrastructural features of lung lesions in sheep dipped in a carbolic dip.

Ultrastructural changes in the lungs of 3 young sheep which became acutely ill with respiratory distress and severe pulmonary lesions 4 to 5 days after dipping in a proprietary carbolic sheep dip consisted of extensive alveolar damage associated with regenerative changes. Damage to alveolar epithelium was associated with accumulations of plasma fluid and cell debris in alveolar spaces, which also contained neutrophils and macrophages. Concurrently, damage to capillary endothelium resulted in liberation of plasma fluid and erythrocytes into the tissues and alveoli. Interstitial oedema was also present. Regeneration took the form of hyperplasia of type II alveolar epithelial cells, many of which were in mitosis, and which often lined alveolar spaces completely. Many of these cells were undergoing early metaplasia into type I pneumocytes, as shown by the development of elongated cytoplasmic extensions which increased the thickness of the blood-air barrier. Interstitial fibrosis was not a prominent feature. It is presumed that these effects resulted from skin absorption of an unknown toxic substance in the dip.