STUDIES BASED ON A MALIGNANT TUMOR OF THE RABBIT : IV. THE RESULTS OF MISCELLANEOUS METHODS OF TRANSPLANTATION, WITH A DISCUSSION OF FACTORS INFLUENCING TRANSPLANTATION IN GENERAL.

The results of seven methods of transplantation of a malignant tumor of the rabbit are reported and contrasted with results obtained by intratesticular inoculation. It was found that inoculations made into the brain, the anterior chamber of the eye, and the muscles gave an almost uniform series of takes with the production of comparatively large and vigorously growing tumors. Intracutaneous inoculations were less favorable, while with subcutaneous, intravenous, and intraperitoneal inoculations, a growth was obtained in only 20 to 25 per cent of the animals. In contrast with the malignant course of the disease produced by testicular transplantation, the tumors produced by methods other than intracerebral inoculation were relatively benign. In all cases, the growth was of a purely local character; in some instances, there was invasion of the surrounding tissues with local or regional extension of the growth, but no metastases developed in distant organs. Tumors in the brain soon caused death as a result of pressure, and the ultimate fate of tumors in the eye was not determined, but the growth produced by other methods of local inoculation was of relatively short duration and terminated with spontaneous resolution. It was found that while a good growth could be obtained with material which had been subjected to repeated freezing, thawing, and grinding, the use of cell-free filtrates or desiccated tumor tissue gave negative results. In discussing the experiments reported, it was pointed out that there were three groups of factors which had played important parts in determining the results of transplantation. These were the capacity for growth of the tumor cells, animal resistance, and the advantage given the tumor or the animal by the use of a particular method of inoculation. From an analysis of the results obtained with reference to the operation of these factors, the conclusion was reached that while the quality of malignancy displayed by the tumor was conditioned upon the capacity for growth of the tumor cells, the degree of malignancy exhibited in any given instance was a function of animal resistance which was not entirely specific but corresponded closely with the ability of the animal to meet excess demands arising from other causes and, to this extent, represented an expression of the functional capacity of a mechanism which is concerned primarily with the maintenance of the general animal economy.