294 INFECTION AND IMMUNITY 



the antibodies, free in the serum, are identical with the receptors 

 of the body cells upon which the antigen originally acts. 



In regard to agglutinins, Ehrlich, as we have seen, believes that 

 it is the agglutinin itself which, first uniting with its antigen by 

 its haptophore group, then causes clumping by its zymophore group. 

 Now, as a matter of fact, Bordet 45 has shown that it is not the 

 agglutinin itself which agglutinates, but that agglutinin with its 

 antigen forms a complex which is then agglutinable by the salt 

 present in the solution. This conclusion seems borne out by the 

 later work of Gengou, 46 Landsteiner and Jagic, 47 and others, who 

 have shown that bacteria which have absorbed other substances, 

 such as uranium compounds, colloidal silicic acid, etc., are subse- 

 quently agglutinable by salts. In consequence, from these and other 

 observations, Bordet concludes that it is neither necessary nor ac- 

 curate for the explanation of these phenomena, to assume the con- 

 ditions conceived by Ehrlich, but that the phenomenon of agglutina- 

 tion consists primarily of the union of the antibody with its antigen 

 in a colloidal suspension, and that the actual subsequent agglutina- 

 tion is a purely secondary phenomenon which depends possibly upon 

 a change in the physical properties of the emulsion upon "its col- 

 loidal stability." A similar condition he assumes for precipitins. 



Without being able in the limited space available to go into a 

 detailed discussion of the large volume of work which has appeared 

 on this subject, we may say that it is our opinion at present that 

 the evidence largely points in the direction indicated by Bordet, 

 namely, that the essential feature of all these reactions is the specific 

 union of an antigen with its antibody, that thereby the physical 

 or chemical condition of the antigen is so changed that it now 

 becomes less stable and is agglutinated or precipitated by such 

 physical influences as, for instance, the presence of an electrolyte. 

 The work of Neisser and Friedmann 48 has shown that bacteria that 

 have absorbed agglutinin are agglutinated by concentrations of salt 

 far less than is necessary to agglutinate or precipitate the normal 

 bacteria. 



Our own opinion, set forth in a number of experimental studies, 

 would go even further than this. We incline to the belief that all 



4r> Bordet, Ann. de Pinst. Pasteur, 1899. 



46 Gengou, Annal. Past., 1904. 



47 Landsteiner mid Jagic, Wien. klin. Woch., iii, 1904. 



48 Neisser and Friedmann, Munch, med. Woch., 1904, li. 465-827. 



