Types of meningococci have been subjected to ultraviolet treatment and changes in antigenic properties observed. By a technic of agglutinin absorption it has been shown that such modifications are attributable to the physicochemical action of the rays.

Carefully regulated exposures which exclude the influence of heat on the bacterial proteins exert a definite action on the cells. Such treatment appears to favor agglutinin response and to diminish the toxic effects of certain organisms.

The group relationships of bacterial types are brought out quite clearly when under the influence of a physicochemical agent which “unlocks” or alters antigenic properties within the cell.

The action of ultraviolet rays on micro-organisms as observed in these experiments suggests a method for building up an immunity in animals by injections of bacteria exposed to the rays for constantly diminishing periods of time. The importance of working below the lethal dose of ultraviolet rays is obvious.

Certain types of bacteria while supposedly containing only a major antigenic structure actually contain minor antigens also.

There is evidence that a few strains, or probably a single strain of bacteria may suffice for immunizing against a heterogeneous group of organisms.

The experiments suggest that a single protein (antigenic) structure represents the element common to groups of biologically related organisms.

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