226 A MAMJAL OF BACTERIOLOGY 



marked feature. In the latter instance, the red corpuscles 

 extravasated into the pulmonary alveoli probably act as 

 antigen and five rise to the production of " erythrocyte 

 agglutinin." 



Substances are also present in bacterial cultures 

 which give rise to agglutination of the organisms of the 

 culture. Thus, the filtrate of a week -old typhoid broth 

 culture will agglutinate typhoid bacilli. These agglu- 

 tinating substances are probably quite different from the 

 immune agglutinins of an agglutinating serum. 



The mechanism of agglutination and the manner in 

 which it is brought about may now be considered. 

 Agglutinin is a relatively stable substance, and an agglu- 

 tinating serum retains its activity for long periods, 

 deteriorating slowly. Heating to 56 C. does not destroy 

 agglutinin, so that it has nothing to do with complement, 

 which takes no part in its action. Ehrlich regarded 

 agglutinin as a receptor of the second order (see p. 184), 

 possessing a haptophore group and an ergophore group. 

 As is generally the case, the haptophore is the more stable 

 (cf. toxin), and by heating agglutinating serum to 

 70-75 C. the ergophore group is destroyed, so that it 

 no longer agglutinates, but the haptophore group remains, 

 and the heated non-active agglutinin is still capable of 

 uniting with the homologous bacterium. This is demon- 

 strated by the fact that bacteria treated with heated 

 agglutinin no longer agglutinate with an active serum 

 the heated agglutinin has been absorbed by the bacteria, 

 the haptophore group remaining intact and saturating 

 the receptor group of the bacterium, so that the active 

 agglutinin cannot become attached. The inactive agglu- 

 tinin retaining the haptophore group may be termed 

 " agglutinoid " (cf. toxin and toxoid). 



Two stages may be distinguished in the act of agglu- 

 tination, first absorption and fixation of the agglutinin 



