THE UNIQUENESS OF THE INDIVIDUAL 



be transferred from one mouse to another by transfusions of 

 blood or serum, for all that the blood may contain a high 

 concentration of antibodies. A second is that the blood of an 

 animal which has received and rejected a homograft contains 

 nothing that opposes or even discourages the growth of a 

 donor''s cells in tissue culture. A third has emerged from some 

 ingenious work carried out at the National Cancer Institute 

 in the U.S.A.^ If a donor^s cells are grafted into an animal 

 which has been forearmed against them, by having received 

 and rejected cells of the same origin before, they are promptly 

 set upon and destroyed. But if the donor's cells are housed 

 inside a little permeable plastic bag within the recipient, then 

 they will be destroyed if, and only if, the walls of the bag are 

 permeable enough to let through the recipient's cells. Perme- 

 ability to molecules of the size of antibody molecules is not 

 enough. Clearly, then, it is not sufficient merely to confront a 

 donor''s cells with antibodies. Is it even necessary to do so.'^ 

 Apparently not, for the following reason. A donor's tissue, 

 lying in a plastic bag that is permeable to antibodies but not to 

 cells, will be destroyed if cells from the immunized recipient 

 are added to the contents of the bag before it is sealed up and 

 introduced into the recipient. This experiment reproduces the 

 state of affairs in which the donor's tissue is housed in a plastic 

 bag that is permeable to the recipient's cells, the only difference 

 being that, in this variant, the recipient's cells are spared the 

 exertion of getting in. But the donor's tissue is also destroyed 

 if the bag and its contents are grafted into the donor or an 

 animal genetically similar to the donor. The donor's body 

 fluids may well contain something necessary for the immuno- 

 logical reaction to take effect within the plastic bag, but what- 

 ever that may be, it cannot be an antibody, for the donor 

 cannot contain antibodies acting against its own cells. 



1 J. M. Weaver, G. H. Algire and R. T. Prehn, /. National Cancer Inst., 

 15, p. 1737, 1955. 



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