722 ANTIGENIC PROPERTIES OF THE BACTERIAL CELL 



for example, antibody formation is a regular response to the parenteral administra- 

 tion of coagulable proteins and cellular antigens, while no demonstrable true anti- 

 bodies have so far been detected in many so-called "idiosyncrasies "and "allergies." 

 Fundamentally, however, all of these occurrences are alike in depending upon specific 

 changes in cell response; and in so far as these are concerned, their manifestations 

 show close analogy — differing only in those phases in which the presence of circulating 

 antibodies is' significant (passive sensitization, etc.). 



It has seemed to us particularly important to extend the antigen conception in 

 this manner in a discussion involving bacteria; for the bacterial cell, as we shall see, 

 contains a variety of biologically active materials, some of which are truly antibody- 

 inducing substances in the older sense of the word — others, however, like the active 

 substance of tuberculin and its analogues, inciting profound and speciiic effects upon 

 the tissues without necessarily giving rise to demonstrable circulating antibodies. 

 In speaking of the antigenic materials of the bacterial cells, therefore, we shall employ 

 the word as signifying all substances which arouse specific reactions in the body of the 

 host, whether these involve true antibody formation or not. 



In infectious disease, then, we have a specific instance in which the foregoing 

 physiological process is set in motion, but complicated beyond similar phenomena by 

 the fact that the antigen is capable of multiplication within the host and at the host's 

 expense. In the last analysis, all immunological reactions, both those between the 

 antigen and the cell as well as those between the antigen and its antibody, must be 

 dependent upon chemical afi&nities. Both the facts of specificity and studies upon the 

 modification of antigens by chemical manipulations have made this clear. But, as in 

 enzyme chemistry,' we are as yet dependent upon indirect experimental methods be- 

 cause no adequate chemical definition of the reacting substances is possible. Never- 

 theless, it is necessary — even though in a rudimentary manner — to approach the 

 problem by an attempt to correlate the chemical structure of the bacterial cell with 

 the immunological responses of the infected or immunized animal. 



in favor of the likelihood of the essential identity of antibodies induced by the same antigen but appar- 

 ent by different activities in different systems. In connection with this we suggested a purely' con- 

 venient differentiation between the antigens leading to sensitizing antibodies and those inducing 

 antitoxins. The purpose of establishing a conception of antito.xinogen was merely to simplify a 

 practical bacteriological distinction between antigens that can be expected to produce neutralizing 

 antitoxic substances and those by which sensitizing antibacterial reaction bodies are produced. In a 

 recent paper, Neill, Fleming, and Gaspari have pointed out that there need be no real difference be- 

 tween the mechanism of the. immunity responses induced by the antitoxinogens and sensitizing 

 antigens, which is quite in conformity with our own conception of antibody production as a manifes- 

 tation of a common biological response to foreign protein. They say: "The usual distinction between 

 the two types, of antibodies (antitoxins and sensitizing antibodies) depends upon differences between 

 the properties of the antigen-antibody compounds and the properties of the specific antigens. With 

 the toxin-antitoxin compounds, the proniiiioit change is in pharmacological properties; with the other 

 antigen-antibody compounds, it is iisuall}' a change in physical properties." And again, "In a certain 

 sense, 'neutralization' as well as 'agglutination' can be considered as a phenomenon secondary to the 

 actual combination of antigen and antibody," both of them representing methcids of detecting antigen 

 antibody union rather than criteria of deep-seated diff'erences between two types of antigens or two 

 types of antibodies (Neill, J. M., Fleming, W. L., and Gaspari, E.L.: /. Exper. Med., Nov., 1927). 

 ' For the most recent authoritative discussion of these points see Wells, H. G.: The Chemicu! 

 Aspects of Immunity {Mono. Am. Chem. Soc). 1925. 



