1907.] Phenomena exhibited by Precipitin Antisera. 469 



shown that, after the interaction of 0*001 c.c. or 0'005 c.c. homologous protein 

 and O'l c.c. antiserum, the addition of further quantities of antiserum 

 produces a fresh deposit proportional to each added mass of precipitin.* 

 This is strongly suggestive that, after each interaction, unoccupied binding 

 affinities of the homologous protein are available. Further, if inhibition is 

 produced by the binding of the thermostable haptophorous groups of the 

 heated antiserum to receptors of the protein molecule, it is remarkable that 

 the addition of considerable masses of homologous protein fails to provide 

 receptors for the precipitin groups of the unheated antiserum and to bring 

 to an end the inhibition. 



All that we can say is that inactivation and inhibition are separable 

 phenomena, commonly appearing together because of the proximity of their 

 respective temperatures of origin, and depending on substances whose 

 interactions do not admit of. so simple an expression as that afforded by the 

 usual statement of Ehrlich's theory. 



Specificity of the Inhibition exercised by Heated Antisera : Phenomena of 



" Crossed " Inhibition. 



The non-appearance of a precipitate in an otherwise effective precipitin 

 interaction is not always due to the same conjunction of chemical and 

 physical factors, and of these factors some exert an inhibitory influence that 

 is altogether non-specific. But the inhibitory power of heated antiserum 

 is markedly specific, probably not less specific than the reaction of the 

 corresponding unheated antiserum. The nature of this specificity is best 

 illustrated by a concrete example. Thus, a heated hen-egg antiserum will 

 prevent the formation of a precipitum between hen-egg albumin and any 

 hen-egg antiserum, but not between ostrich-egg albumin and ostrich-egg 

 antiserum, nor will it have any effect on non- avian precipitin interactions. 

 The phenomena of " crossed " inhibition are revealed by the fact that heated 

 hen-egg antiserum will inhibit precipitation between hen-egg albumin and 

 ostrich-egg antiserum and between ostrich- egg albumin and any hen-egg 

 antiserum. Moreover, when ostrich-egg proteins were substituted for the 

 corresponding hen-egg proteins in each of the above experiments, identical 

 results were obtained. These results may be summarised in the following 

 Table I :— 



* Welsh and Chapman, ' Eoy. Soc. Proc.,' B, vol. 78, p. 305, 1906. 



