268 INFECTION AND RESISTANCE 



alyses of quantitative relationships, both of agglutinin and precipitin 

 reactions, that these take place according to the laws of mass action. 

 In consequence, in addition to the combined precipitin-antigen com- 

 plex present in all mixtures of the two, there should also, be present 

 free dissociated fractions of each, in amounts dependent upon rela- 

 tive concentrations. This might explain conditions such as those 

 described above. 



Yon Dungern, whose paper forms one of the most extensive studies 

 of the phenomenon with which we are concerned, does not believe 

 that precipitin reactions can follow the laws of mass action, and 

 explains the simultaneous presence of precipitin and antigen in the 

 same serum by assuming a multiplicity of precipitins. He believes 

 that every proteid antigen contains a number of related partial an- 

 tigens which give rise in the immunized animal each to a partial 

 precipitin. In sera in which both antigen and precipitin are found 

 side by side and free, he believes that the antigen is of a nature that 

 has no affinity for the particular partial precipitin present with it. 

 He says : "Auch hier handelt es sich nicht um zwei reaktionsf ahige 

 Korper, deren Verbindung aus irgend welchen Griinden unterbleibt, 

 sondern um Substanzen, welche keine Affinitat zu einander besitzen. 

 Die betreffenden Kaninchen haben zu dieser Zeit noch nicht alle 

 mb'glichen Teilprazipitine gebildet, sondern nur einzelne derselben. 

 Diese zunachst produzierten, nur auf bestimmte Gruppen der prazi- 

 pitablen Eiweisskorper passenden Partialprazipitine sind es, welche 

 nach der Absattigung aller zur Yerfiigung stehenden zugehorigen 

 Gruppen der prazipitablen Substanz in Serum nachweisbar werden. 

 Daneben bleibt aber ein anderer Teil der prazipitablen Substanz, 

 der keine Affinitat zu dem gebildeten Prazipitin bestizt, bestehen, 

 solange bis ein anderes Partialprazipitin von den Kaninchenzellen 

 geliefert wird, welches sich mit Gruppen der in Losung geliebenen 

 Eiweisskorper vereinigen kann." 



Zinsser and Young 57 have also studied these phenomena and 

 have attempted to explain them on the basis of protective colloidal 

 action. In considering the theories that have been advanced to ex- 

 plain these occurrences, the conception of mass action as accounting 

 for the simultaneous presence of the two reacting bodies in the same 

 serum seemed entirely incompatible with our own observations and 

 with those of Gay and Rusk, that these sera do not of themselves 

 fix alexin. Were the conception of the manner of union of these 

 two reagents, according to the laws of mass action, representative 

 of the true state of affairs, it would be necessary to assume the pres- 

 ence, in such sera, not only of the two reacting bodies free and disso- 

 ciated, but also of a definite quantity of the united complex of the 

 two, a state of equilibrium being established. If this were the case 

 the sera should, in agreement with all experience on the phenomenon 



57 Zinsser and Young. Jour, of Exp. Med., 1913, Yol. 17. 



