THE UNIQUENESS OF THE INDIVIDUAL 



same inbred strain, the second mouse behaves exactly as if it 

 had itself been actively immunized beforehand, i.e. as if it had 

 received and rejected a homograft before. This is analogous to 

 passive immunization with an antiserum in the sense that it is 

 the first mouse which undertakes the reaction against the 

 homograft and the second which shares the benefit of it. But 

 it is not exactly analogous, because the transference of the state 

 of immunity cannot be brought about by injecting the first 

 mouse''s blood or blood serum into the second; it must be the 

 first mouse''s living lymph node cells. 



This is the first sign of an important difference between the 

 immunity caused by bacteria (or other remotely foreign anti- 

 genic substances) and the immunity caused by living cells 

 originating from some other member of their recipient''s species. 

 There can be no doubt that antibodies are the chief instru- 

 ments of the defensive reaction against what may be com- 

 pendiously described as ""germs'. It is true that antibodies 

 themselves do not seem to do bacteria much harm; what they 

 do is to make the bacteria particularly palatable to phagocytes, 

 or to make them sensitive to the action of a complex con- 

 stituent of the blood known as 'complemenf, which dissolves 

 them. But although antibodies may not be sufficient to bring 

 about the destruction of bacteria, they are certainly necessary; 

 yet in the reaction against skin homografts there is no clear 

 evidence that they are even necessary. 



The highly skilled researches of Dr P. A. Gorer of Guy''s 

 Hospital have shown that antibodies are certainly formed when 

 a homograft of skin or of tumour cells is reacted upon and 

 sloughed away. The antibodies are of a chemically quite 

 orthodox kind, and may be recognized by their power to 

 agglutinate the red blood corpuscles of the donor. If antibodies 

 are formed, why should we doubt that they are the chief 

 eff'ectors of the immunological response? 



The main reason, perhaps, is that a state of immunity cannot 



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