THE UNIQUENESS OF THE INDIVIDUAL 



When exposed for the first time to a homograft or a disease- 

 producing organism, an animal takes the homograft or may get 

 the disease. Resistance develops in the course of exposure — the 

 disease is got over, the homograft sloughs away — and now, for 

 many months, the animal becomes refractory, and will not get 

 the same disease or take a graft of the same kind again. As to 

 the specificity of the reaction, here too there is an exact 

 analogy, for recovery from one disease will not prevent oner's 

 succumbing to another unless, as with cowpox and smallpox, 

 the organisms that cause them are closely related; and so it is 

 with homografts, as I have just explained. 



It has been known for many years that bacteria which gain 

 a foothold in the skin may enter the lymphatics, the system of 

 vessels responsible for the fluid drainage of the tissues, and so 

 enter the lymph nodes which lie athwart every lymphatic vessel 

 somewhere between its source in the tissues and its final out- 

 flow into the veins. Lymph nodes, less properly lymph ''glands'', 

 are the organs in the neck and armpit and elsewhere which 

 people refer to when they say their 'glands'" are swollen; and 

 lymph nodes are probably the first places in the body in which 

 antibodies are made. Antibodies made in one animal can be 

 injected into another, so conferring upon it a vicarious, 

 ''passive'' or second-hand immunity. In medical practice, for 

 example, antibodies against the toxins of tetanus or diphtheria 

 organisms are commonly made in horses. The horse''s serum, 

 now an antiserum, can then be injected into human beings. 



The reaction against homografts is much the same. Anti- 

 genic substances from the homografts reach the local lymph 

 nodes, normally via the lymphatics, and the local lymph nodes 

 are the principal seat of the recipient ''s reaction. Mitchison^ 

 has shown that if cells are taken from the lymph nodes of a 

 mouse which has been actively immunized against a homograft, 

 and if these cells are then injected into a second mouse of the 

 1 N. A. Mitchison, Proc. Roy. Soc. B, 142, p. 72, 1954. 



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