212 MICROBES AND TOXINS 



Antitoxin does not destroy toxin because the two reacting 

 bodies can be recovered. For example, the neurotoxin of 

 cobra venom resists heating to 68° C. ; when the neutral mixture 

 of venom and anti-venom is heated, the toxin can be recovered 

 if this isdoneduring the ten minuteswhich followthe preparations 

 of the mixture (Calmette's experiment). From a neutral mixture 

 of cobra-haemolysin and anti-venom, it is possible to recover the 

 haemolysin by the action of hydrochloric acid ; the recovered 

 hgemolysin manifests its action on the addition of the necessary 

 lecithin (Morgenroth's experiment). A mixture of diphtheria 

 toxin and antitoxin (twenty-four hours' contact), harmless to 

 the rabbit, recovers its toxicity when treated with hydrochloric 

 acid, the toxin being set free (Morgenroth and Willanen's 

 experiment). Heat, filtration, the action of a digestive diastase, 

 are other methods of dissociating the toxin-antitoxin com- 

 bination provided the intervention takes place without too 

 long delay. 



How then are the toxin and anti-toxin to be represented ? 

 Probably as albuminoid substances of large molecules capable 

 of being represented by stereochemical models and possessing 

 a nucleus on which are grafted lateral chains. To conceive of 

 the action of the toxin on a cell, it is only necessary to imagine 

 the molecules of the cell protoplasm as containing figures of 

 the same kind. The toxin molecules enter into relation or 

 combination with the cell molecules by means of these atom 

 groups or side-chains. Ehrlich calls them " receptors " 

 or " haptophorous groups." The term " side-chains " was 

 borrowed directly from the chemistry of benzene. Such 

 stereochemical symbols were introduced into science by Emil 

 Fischer to represent the specific action of the ferments : one 

 body acts specifically on another, because an atom group of 

 the one is adapted to an atom group of the other, as with a 

 key and the corresponding lock. Thus the haptophorous group 

 of a toxin fixes itself on the receptor of a cell, both haptophore 

 and receptor being " side-chains." 



This in fact is the central idea of the theory, the same mode 

 of chemical action, the same relations between receptors and 



