NATURE OF ANTIBODIES 199 



according to the unitarian theory a single antigen, in a pure state, 

 would stimulate the formation of one variety of antibody capable 

 of uniting with the antigen. This union of antigen and antibody 

 could result in agglutination, precipitation, complement fixation, 

 bactericidal phenomena, opsonization or anaphylactic sensitization 

 depending upon the physical state of the antigen itself, "tlie na- 

 ture of the cooperative substances (alexin, leucocytes, tissue cells) , 

 and by the environmental conditions under wliich tlie observations 

 are made." Delves (1937) as well as Zinsser, Enders and 

 Fothergill (1939, pp. 175-178) cite considerable experimental evi- 

 dence in support of this theory. 



While it has been apparently established that an antigen may 

 give rise to more than one antibody, yet it is conceivable that 

 any one of the antibodies may serve some or all of tlio various 

 capacities mentioned by Zinsser. It is possible, as suggested by 

 the work of Horsfall and Goodner mentioned earlier in this cliap- 

 ter, that antibodies from some species of animals may not promote 

 complement fixation although they lead to precipitation. Witli 

 these points in mind we are accepting the general tenets of his 

 Unitarian theory until more evidence against it is available. 



Mechanism of Antigen-Antibody Union. — There are at least 

 two theories explaining antigen-antibody union that are being dis- 

 cussed at present. According to the film hypothesis supported 

 by Eagle, Mudd and others, the antibody is specifically adsorbed 

 to the antigen forming a partial or com])le1e film on the surface. 

 The antibody globulin becomes insoluble in saline (denatured) 

 as a result of this union with antigen. Eagle suggests that the 

 specificity of the antibody globulin is due to its hydrophilic 

 (water-loving) groups which become attached to the antigen, thus 

 orienting the hydrophobic ends of the molecules outward toward 

 the water which accounts for the denaturing of the antibody pro- 

 tein. Marrack, on the other hand, cites the quantitative studies 

 of Heidelberger and Kendall as offering evidence against the film 

 hypothesis. He thinks the antibody molecule combines as a closely 

 packed group of molecules and not as a film. As a working 

 theory we are tentatively accepting the film hypothesis as out- 

 lined by Eagle and also Mudd. 



There are also two lines of thought relative to the mechanism 

 of agglutination and precipitation which may result from antigen- 



