THE INTERACTION OF ANTIGEN AND ANTIBODY IN AGGLUTINATION. A STUDY BY ELECTRON MICROSCOPY.

Flagellar fragments are thin cylinders that are particularly suitable for the study of agglutination by electron microscopy. Their shape leads to a characteristic pattern of agglutination and thus the early stages can be studied. Measurement of interflagellar distances under conditions of negative staining, suggest that the minimum length of the rabbit antibody molecules is about 180 Å. The molecules carry the specific sites at the ends of the long axis, and become attached radially to the surface of the flagella, resembling the bristles of a bottle-brush. To explain this orientation it is postulated that the antibody is inserted into the surface of the flagellum in such a manner that surrounding molecules give it a fixed direction. Geometrically this hypothesis corresponds to an insertion into pits. Pepsin-treated (5S) rabbit antibody behaves in a like manner, but the molecule appears to be shorter. No information could be obtained about the thickness and actual shape of antibody molecules by the techniques employed.