516 STUDIES IN" IMMI MI'V. 



with an energetic affinity for one another, in which case the reaction 

 is complete and gives rise to a relatively stable compound I Ehrlich), 

 or between Bubstances with weak affinities, in which case the com- 

 bination is only partial and distinctly reversible; a state of equili- 

 brium in Other words would be established between | he fraction of 

 the antigen which remains free and theone which enters into com- 

 bination (Arrhenius and Madsen). According to other authors, 

 and 1 believe I was the first to offer this opinion, the union of the 

 antibody with the antigen depends on what is called molecular 

 adhesion or contact affinity, in other words should be classed in the 

 category of adsorption phenomena.* 



In this connection it is well to define the limit of the debate and 

 avoid misunderstandings. The phenomena of adsorption are fre- 

 quently contrasted with true chemical phenomena, but it is not the 

 function of the biologist to define the frontiers of physics and chem- 

 istry. What is more, this task is no easy one, since the most au- 

 thoritative physical chemists, as Van Bemmelen, Nernst and many 

 others, themselves consider that there are all transitions between 

 data of adsorption and those of true chemical combination. It is, 

 then, superfluous for me to defend myself again, as I have already 

 done in one of my articles, against criticism that has been raised 

 against me on the ground that I deny definitely any chemical 

 character to the union of antibody and antigen by classing them 

 among adsorption phenomena. When in discussing the action of 

 sera one mentions, indeed, as an example, the dyeing of a piece of 

 filter paper by an anilin dye, it is not the purpose to find out whether 



* Inasmuch as it is not possible to give a complete historical account at this 

 time, I may confine myself to citing what Ulrich Friedemann has published in the 

 beginning of his remarkable work, "Ueber die Fallung von Eiweiss durch andere 

 Kolloide und Ihre Beziehungen zu den Immunkorperreaktionen," an historical 

 account which deals with the first articles bearing on the relation of adsorption 

 to immunity. 



" Das Studium der Kolloide hat bereits vielfache Aufschlusse fiber die physi- 

 kalisch-chemischen Vorgange bei der Immunitatsreaktionen gegeben. Die 

 Verbindungen der Immunkorper wurden mit den Adsorptionverbindungen der 

 Kolloide vergleichen (Bordet, Landsteiner und Jagic, Biltz, Zaugger, Much und 

 Liebert, Pauli), wahrend sich eine bemerkenswerte Ahnlichkeit zwischen 

 den Fallungsreaktionen der Immunkorper (Agglutination und Prazipitation) 

 und den Gelbildungen und Prazipitations-erscheinungen in Kolloidaler Losungen 

 und feiner Suspensionen herausstellte. (Bordet, Bechhold, Xeisser und Friede- 

 mann, Biltz, Landsteiner und Jagic, Henri und Mitarbeiter, Gengou.)" 



