Chapter Ip 



The Relations Between Age and Individuality 



Differentials 



The French surgeon, Oilier, observed, during the latter half of the 

 last century, that autotransplants of skin and periosteum grew much 

 better in young than in older individuals, where they grew only 

 temporarily. Also, Schoene noticed that old age is unfavorable for trans- 

 plantation of skin and that in old rats even autotransplantation may yield 

 bad results. Kozelka found, in transplantation of skin into fowl, that the 

 adult host had greater resistance to grafts of strange skin than the chick 

 and that also the adult tissue is less able to adapt itself to an adult host 

 than the young tissue to a very young host, and furthermore, that young 

 grafts in young hosts remain alive or regress only slightly when the host 

 becomes older. He assumed that the milder form of tissue antagonism present 

 in the host enabled it to eliminate the incompatible elements, without totally 

 destroying the tissue. According to Pfeiffer, the gonads of immature animals, 

 and especially those of immature rats, take more readily than those of adult 

 rats. On various occasions we have compared the reaction against strange 

 grafts in young and in older rats and guinea pigs. In the young, inbred 

 King rats the reaction against transplants of various tissues was milder than 

 in older rats, and not only against transplants within the inbred strain, but 

 also against those from hybrids, in which latter a constituent had entered 

 which was strange to the member of the inbred parent strain serving as 

 host. In experiments in mice we had observed that in somewhat older mice 

 the reaction against the transplant was, in certain cases, stronger than in 

 very young mice, although this did not need to be the case in all experiments. 

 In older mice, from 10 months to 20 months old, transplants of various 

 tissues from younger animals could be as well preserved as in younger hosts, 

 and the reaction was not noticeably more severe in these old mice than in 

 younger adult mice. 



There remains the problem as to the mechanism by means of which age 

 affects the transplants and in this respect experimental evidence is as yet 

 slight; it will be necessary especially to consider separately the effect of age 

 on the host and on the transplanted tissue. If even in autotransplantations, 

 skin and bone grafting is less favorable in older than in younger individuals, 

 this is possibly due to the better vascularization and to the greater tendency 

 of the connective tissue to remain more cellular and less fibrillar in younger 

 organisms. This condition seems to be independent of the reaction of the 

 individuals serving as donors and as hosts against strange individuality dif- 

 ferentials ; it is related, in all probability, to the fibrous changes in the stroma, 



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