Two cutaneous papillomas produced with the Shope virus in adult domestic rabbits were transferred to their leg muscles and thence to those of several successive groups of rabbits of various ages. The growths failed to establish themselves in some newborn animals, but in many formed huge masses, immobilizing the legs with result in early death. Not infrequently they did well for months after their hosts had matured, yet nevertheless they failed regularly on further transfer in adults. They were eventually lost because left long prior to passage on the supposition that they might gain the ability to succeed in mature hosts.
The papillomas when growing actively sometimes penetrated the reactive tissue encapsulating them and replaced the adjacent muscle. They often entered lymph and blood vessels but never metastasized, nor did they undergo carcinomatous change though their total period of proliferation was as considerable as that elapsing in many instances before cancer appeared in papillomas produced by the same virus material and left on the skin.