398 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



cells to a different type of host was produced experimentally, or in other cases, 

 the reactivity of the host against the cancerous transplants was diminished 

 through injection of substances which in all probability inactivated the 

 reticulo-endothelial system of the host. We have also referred to experiments 

 in which the reactions of the host against transplanted cartilage became 

 weaker in the course of time, thus indicating possible processes of adaptation 

 which took place in the host under the influence of the transplant. Quite 

 recently, Cloudman has published some experiments which point perhaps in 

 the same direction. He found that an osteogenic sarcoma, which had originated 

 in the tail of a C57 mouse and grew in 100 per cent of C57 mice inoculated 

 with this tumor but grew in a much smaller percentage in D mice, took in a 

 somewhat larger percentage of D mice which had been transferred at the 

 beginning of their embryonal development into the uterus of C57 mice and had 

 undergone further developments here instead of in the uterus of their real 

 mother. While this treatment increased the number of successful inocula- 

 tions and also the rapidity of growth of the transplanted tumors, the 

 growth of the sarcoma was not decreased thereby in C57 mice which had 

 developed in the uterus of D mice. Corresponding results were obtained 

 in experiments with a malignant melanoma which had originated in the 

 tail of a D mouse, and perhaps also in experiments in which Law increased 

 by means of foster-nursing the number of successful transplantations of 

 leukemic cells in mice belonging to a subline of the D strain, which differed 

 from the one in which the leukemia had originated and which was less favor- 

 able for the transplantation of the leukemic cells possessing a different 

 individuality differential. It is possible that the transfer of substances possess- 

 ing a different individuality differential by way of the uterus or by way of the 

 milk of the mother caused an adaptation of the host against these substances, 

 which was thus rendered more tolerant against the strange individuality differ- 

 ential of the tumor cells. But it is also possible that the substance thus trans- 

 ferred into the mice serving as hosts supplied the latter with a carrier of the 

 individuality differential more closely related to that of the tumor cells which 

 the latter needed for a successful growth, or that substances introduced into 

 the future hosts by way of the uterus or with the milk of the nursing mother 

 supplied the hosts with an agent which stimulated the growth of the sub- 

 sequently transplanted cells. There are indications that the effect observed in 

 these experiments is only a temporary one ; mice which were inoculated with 

 the tumor several months after they had received the strange substance no 

 longer reacted favorably to the transplanted tumor. However, it is not yet 

 certain whether this loss of tolerance was due to the older age of the mice 

 under these conditions, or whether it was due to the fact that the strange sub- 

 stance was gradually eliminated. All these experiments taken together do not, 

 therefore, suggest that variations in the growth energy or in the percentage 

 of successful transplantations of a tumor are due to changes in the organismal 

 differentials in the host or in the transplant; but they point to the presence 

 of factors, which, when added to the action of these differentials, may modify 

 the mode of the reaction of the host against the transplant. 



