Abstract
Experimentally produced bovine cutaneous papillomas of 30, 76 and 112 days' duration as well as 3 naturally occurring bovine cutaneous papillomas were examined by light and electron microscopy. Degenerative changes were not observed in the fibromatous base of the 30-day-old papilloma. An alteration in all papillomas older than 30 days was cytoplasmic vacuolation in cells of the prickle cell and keratohyaline layers. As cells progressed upward their degeneration became more prominent. In the keratinized layers of 2 papillomas virus-like particles were observed within plasma membranes of keratinized cells.
