184 A MANUAL OF BACTERIOLOGY 



and ultimately these receptors are formed so numerously 

 that numbers of them become free in the plasma (Figs. 29, 

 30). These receptor side-chains, detached from the cell and 

 floating free in the blood-stream, constitute the antitoxin. 

 This excessive production of side-chains after stimulation 

 by repeated injections of toxin is not a phenomenon 

 confined to antitoxin formation, but is a general phy- 

 siological law enunciated by Weigert ; as a result of 

 repeated stimulation, over-production or hyper-compensa- 

 tion is the rule and is met with in various pathological 

 processes. Ehrlich has termed the diverse free receptors 

 which occur in the body fluids in various circumstances 

 " hap tines." 



Ehrlich distinguished three classes of receptors. Receptors of 

 the first order, to which belong antitoxins, which possess a hap to - 

 phore group capable of saturating the affinities of the corre- 

 sponding haptophore group of the homologous toxin ; Receptors 

 of the second order, which have, in addition to their haptophore 

 group, a second or ergophore group which, after union with the 

 antigen has taken place, is able to bring about the changes pecu- 

 liar to the particular type of anti-body. The precipitins and 

 agglutinins belong to this class. Receptors of the third order : 

 In addition to the haptophore group the anti- bodies possess a 

 complementophile group which unites with complement which is 

 necessary to complete the lysis of corpuscle or bacterium (p. 208). 

 The opsonins and the anti- bodies concerned in complement fixation 

 belong to this class. 



The existence of both haptophore and toxophore groups 

 in the toxin molecule is suggested by the following experi- 

 ments. Tetanus toxin injected into the blood-stream 

 of an animal rapidly disappears, within a few seconds of 

 the injection, and even if the animal be at once bled, 

 the blood withdrawn being replaced by fresh blood, 

 tetanus ensues, but not until after the lapse of an incuba- 

 tion period of some hours. The tetanus toxin, therefore, 

 immediately becomes fixed or anchored to the tissues 



