T^1 18 



by Ihe action of heat. The agglutinoid cannot produce agghitination, but it has 

 a stronger affinity for the agglutinable substance of the bacteria than is possessed 

 by the agglutinine, whose action it is, in consequence, able to prevent. In confirm- 

 ation of this view they bring forward Hie statement tliat the greater the destruct- 

 ion of the agglutinine, the more pronounced is the "inhibition zone". But this 

 explanation is inapplicable to the results of oar experiments, which prove clearly 

 that the actual destruction of the agglutinine does not depend upon or stand in any 

 definite relation to the extent of the "zones of inhibited agglutination" . The agglut- 

 inating power of a serum can be much weakened while the "inhibition-zone" is 

 but ill-marked ; and conversely, an extensive inhibition-zone can occur when the 

 destruction of agglutinine has been nil, or when its power has actually been 

 increased by the heating. 



If the question were one of the formation of an agglutinoid at the expense of 

 the agglutinine, then "zones of inhibited agglutination" of equal extent should 

 appear whether bouillon-culture or agar-culture suspensions are agglutinated; but 

 this has been found not to be the case. And a final objection to this view of the 

 origin of the "zones" lies in the fact that they may also appear when it is the 

 bacterial culture that is exposed to heat, and not the agglutinine, and when the 

 quantity of the substance formed by the heat is the same in every test-tube of the 

 series — for each tube contains the same amount (löc.cm.) of the bacterial suspen- 

 sion or culture. 



We are of the opinion that the phenomenon can be partly explained by the con- 

 siderable retardation of the velocity of the reaction producing agglutination. In the 

 process of heating the immune-sera or the bacterial emulsion, compounds are formed 

 which can impede agglutination of an agar-culture suspension when they are present 

 in large amount, and accelerate it when present in small amount; in the latter case 

 the action may perhaps be catalytic in nature. 



The slowing of the velocity with which the agglutination proceeds is best seen 

 when agar-culture suspensions are used. For example, in Series 61, a serum diluted 

 with 9 volumes of normal saline was warmed to 70° for half an hour. Measurement 

 of the agglutination it had produced in an agar-culture suspension after standing 

 for IV4 hrs. at 37°, indicated that the serum's agglutinating power had fallen to V71 

 of its original value; after 2'/2 hrs. at 37°, it appeared to have fallen to V? of its 

 original value; about 18 hours later, its loss of agglutinating power was shewn to 

 have been quite small. In Series 62 the same heated serum was used to agglut- 

 inate a bouillon-culture of B. coli; and Ihe measurements, taken after the lapse of 

 identical periods of time, indicated losses in agglutinating power represented by 

 the figures Vsm, Vim and Vi-2 respectively. 



So the conclusion may be drawn that the velocity of the process of agglutin- 

 ation is retarded far less with bouillon-cultures than willi agar culture suspensions; and 



