704 



THE AMERICAN MUSEUM JOURNAL 



the greater will be the injury to the 

 transplanted tissue; this is especially 

 so in the tissues of the higher animals; 

 it is apparently less so in the phyloge- 

 netically lower organisms. 



In mammals we find that, on the 

 whole, grafts can live indefinitely only 

 after transplantation into the indi- 

 vidual in which the tissues originated 

 (autotransplantation). Some excep- 

 tions occur, however, to this rule — as, 

 for instance, in the case of certain tu- 

 mors, which can live and grow in other 

 individuals of the same species; and 

 perhaps the same may hold good in the 

 case of a few particularly resistant tis- 

 sues. After transplantation into other 

 individuals of the same species (homeo- 

 transi3lantation) tissues usually die 

 after a period of transitory life the 

 duration of which varies in different 

 tissues and different individuals. Even 

 in nearly related individuals, grafts 

 have usually a mere temporary exist- 

 ence, although in most cases they live 

 longer than in individuals of the same 

 species which are not related. It may 

 be that occasionally the transplanted 

 tissue lives in a near relative as well 

 as it does after autotransplantation, 

 but such cases, if they occur at all, cer- 

 tainly represent only a small minority. 

 After transplantation into different 

 species, tissues live a very short time, 

 and they die the sooner the farther dis- 

 tant the species of host and transplant 

 are from each other. In invertebrates, 

 however, grafts may, under certain 

 conditions, live permanently even in a 

 strange species. 



"We have reason to assume that the 

 chemical differences existing between 

 graft and host lead to disturbances in 

 the metabolism, or proper taking care 

 of the food, by the grafted tissues. Af- 

 ter transplantation into different spe- 

 cies (heterotransplantation) these met- 

 abolic disturbances are so marked that 

 the grafted tissues die either directly or 

 after a short duration of life. After 



transplantation into other individuals 

 of the same species some tissues are in- 

 jured by the body fluids of the host to 

 such an extent that they also die as a 

 result of this chemical injury. Others, 

 however, — and this applies especially 

 to certain glandular organs,— suffer 

 only a relatively slight metabolic dis- 

 turbance in the new environment, a 

 disturbance which as such would be 

 perfectly compatible with the life of 

 the tissues. However, this metabolic 

 change in the transplanted cells attracts 

 the lymphocytes of the host, which now 

 invade the graft and help to destroy it ; 

 and, in addition, the connective tissue 

 cells of the host may produce more 

 fibrous tissue around a homeotransplant 

 than around an autotransplant and 

 thus interfere with the nourishment of 

 the graft. 



These two factors bring about more 

 or less gradually the death of the trans- 

 plant in cases in which the body fluids 

 alone would not be sufficiently toxic to 

 produce this effect. In general, the 

 more sensitive a tissue is, the more 

 susceptible it is to the injurious ef- 

 fects of those toxic substances which 

 are present in all homeotransplanta- 

 tions. 



While only autotransplanted tissues 

 can live indefinitely, the temporary life 

 of tissues taken from other individuals 

 of the same species, or preferably from 

 nearly related individuals, may be of 

 great practical importance, inasmuch 

 as it may permit the adjoining host 

 tissue to repair defects in a much more 

 efficient manner than could be accom- 

 plished through grafting of dead mate- 

 rial or tissues taken from different 

 species. The investigator is constantly 

 faced by new problems. Also he is 

 rewarded by new knowledge which 

 promises to throw light on fields which 

 apparently are far removed from that 

 of tissue growth. Thus tissue grafting 

 may serve as a method which helps to 

 clear up problems of immunity. 



