468 Prof. D. A. Welsh and Dr. H. G. Chapman. [Apr. 30, 



01 c.c. heated antiserum mixed with homologous protein for 48 hours was 

 able to prevent precipitation when 0*1 c.c. active antiserum (No. 23 or 

 No. 25) was subsequently added. The inhibition was constant, but 

 incomplete, when 01 c.c. heated antiserum was mixed with 0*1 c.c. active 

 antiserum (No. 25) and homologous protein was simultaneously or 

 subsequently added. The inhibition was complete when 0*2 c.c. heated 

 antiserum interacted with O'l c.c. active antiserum and homologous protein, 

 and was independent of the order in which the substances were added. 



Both by heating to 72° C. and by spontaneous degeneration, therefore, it 

 was possible to obtain antisera which were wholly inactive and yet not at all 

 or only doubtfully inhibitory, and thus to effect a separation of the 

 phenomena of inactivation and of inhibition. In both instances, also, heating 

 to 75° C. so altered the constitution of the inactive, non-inhibitory antisera, 

 that they came to acquire powerful inhibitory properties. 



If inactivation and inhibition were inseparable phenomena, it might be 

 supposed that inactivation was merely a particular manifestation of 

 inhibition, that precipitin was not necessarily altered by heating to 75° C, 

 but that an independent inhibitory substance was developed at that 

 temperature. Our observations render this supposition untenable. 



The mere separation of the phenomena of inactivation and of inhibition 

 might be reconciled with the commonly accepted statement of Ehrlich's 

 theory of the constitution of precipitins by the twofold assumption of 

 a diminution, followed by an increase, in the combining affinities of the 

 haptophores. It might, for example, be assumed that an immediate effect of 

 the weakening or destruction of the ergophorous affinities, resulting in 

 inactivation, would be some weakening of the haptophorous affinities also, 

 whereby molecules of the nature of epi-precipitoid, or precipiton, would be 

 produced. On the analogy of epi-toxoids, or toxons, such epi-precipitoids, 

 or precipitons, having feebler combining affinities than the unaltered 

 precipitin molecules, would be readily evicted by them, and so might give 

 rise to little or no noticeable inhibition of the precipitate. It would be 

 necessary also to assume that heating to 75° C. restored or enhanced the 

 potency of the haptophores, so that epi-precipitoids were transformed into 

 syn-precipitoids or even into pro-precipitoids, having combining affinities 

 respectively equal to or greater than those of unaltered precipitins. We do 

 not see how the presence of epi-precipitoid in the inactive, non-inhibitory 

 antisera described by us can be either proved or disproved, unless the 

 occasional doubtful inhibition above noted is to be taken as an indication of 

 its presence. 



Other facts, however, render this explanation inadequate. It has been 



