Tumoren

A papilloma has been observed in wild cottontail rabbits and has been found to be transmissible to both wild and domestic rabbits. The clinical and pathological pictures of the condition have been described. It has been found that the causative agent is readily filtrable through Berkefeld but not regularly through Seitz filters, that it stores well in glycerol, that it is still active after heating to 67°C. for 30 minutes, but not after heating to 70°C., and that it exhibits a marked tropism for cutaneous epithelium. The activities and properties of the papilloma-producing agent warrant its classification as a filtrable virus. Rabbits carrying experimentally produced papillomata are partially or completely immune to reinfection and, furthermore, their sera partially or completely neutralize the causative virus. The disease is transmissible in series through wild rabbits and virus of wild rabbit origin is readily transmissible to domestic rabbits, producing in this species papillomata identical in appearance with those found in wild rabbits. However, the condition is not transmissible in series through domestic rabbits. The possible significance of this observation has been discussed. The virus of infectious papillomatosis is not related immunologically to either the virus of infectious fibroma or to that of infectious myxoma of rabbits.

The papillomas induced in domestic rabbits with virus procured from cottontails undergo progressive changes in the direction of malignancy when they grow vigorously. From the beginning they exhibit the traits whereby tumors are characterized, and they have malignant potentialities. In seven animals of a group of ten carrying papillomas for more than 200 days, cancer has developed, and in an eighth a tumor of problematic malignancy has arisen. One of the remaining two rabbits died early in the cancer period, and the papillomas of the other eventually retrogressed. Ten cottontails with induced growths of much longer duration have not developed cancer. The malignant tumors have all been acanthomatous in type, and have arisen directly from the papillomas by graded, continuous alterations. These have often gone further after malignancy has been attained, and have eventuated in great anaplasia. Metastasis has been frequent, and transplantation to another host has proved successful. Individual growths have occurred expressive of each stage of the transformation to cancer, as if through a stabilization at this stage; yet despite the variety thus afforded, the tumors must all be looked upon as the consequence of alterations in cells of a single sort, namely epidermal cells affected by the virus, and the alterations themselves have taken a single direction. In the morphology of many of the cancers the influence of the virus is still manifest. The better the papilloma grew, the more likely was cancer to occur, and the greater was the tendency to multiple tumors. In the most favorable rabbits malignant changes took place at numerous locations in the papillomatous tissue, and were imminent at many others. Intercurrent factors had much to do with determining frank carcinosis; and when the tendency to it was not marked their influence sometimes seemed crucial. Analogous instances of a graded alteration from papilloma to cancer are frequent in human pathology. The virus that gives rise to the rabbit papillomas must be looked upon as the primary cause of the cancers developing therefrom. Whether it is their proximate cause has yet to be determined.

A tumor-like condition has been observed in a wild cottontail rabbit and has been found to be transmissible to both wild and domestic rabbits but not to guinea pigs, white rats, white mice, or chickens. The clinical picture of the experimentally produced condition and the pathological picture of the original and experimentally produced tumors have been described. The tumor has the general appearance of a fibroma. Methods used in transmitting the condition and satisfactory routes of inoculation have been described and discussed.