LACK OF IMMUNOLOGICAL REACTIVITY 



type of immune response. The intensity of this may, 

 however, vary within very wide Hmits. 



Under special circumstances, foreign tissues can be 



implanted in adult animals and persist. The significant 



examples are (a) corneal transplantation which appears 



to depend in part on low intrinsic antigenicity of 



corneal tissue (Bacsich and Wyburn, 1956) and in part 



on the absence of blood vessels in both host and graft 



tissues (Billingham and Boswell, 1953); {b) endocrine 



transplants to the anterior chamber in an animal from 



which the corresponding endocrine organ has been 



excised (Woodruff and Woodruff, 1950); {c) some 



malignant tumours. 



(v) Tolerance is most readily shown when implanted alien 



cells can persist from embryonic to adult life. By 



appropriate injections in utero or in ovo, partial tolerance 



to non-cellular antigens can be produced in some 



instances, particularly if the injections are maintained 



at short regular intervals during the early weeks of 



the free life of the animal (Dixon and Maurer, 1 955) . 



With some antigens, no success whatever is obtained 



in experiments aimed at achieving immunological 



tolerance. 



(vi) There are many conditions in which abnormal 



destruction of body components, particularly red cells 



or platelets, can be shown to be due to the activity of 



antibody-like agents produced by the body. There is 



no evidence of abnormal antigenicity in the ' target ' 



cells in these cases and opinion is, on the whole, on 



the side of regarding the ' auto-antibody ' as a product 



of a disordered set of antibody-producing cells. 



An overall summary might be that during embryonic life 



a process of mutual interaction between body constituents 



leads to the situation by which in subsequent post-natal life 



no antibody globulins capable of reacting with accessible 



body components are produced. Immune reactions, in- 



35 3-2 



