122 THE SIDE-CHAIN THEORY 



as uniceptors. The receptors of the third order, on the other hand, 

 possess two combining groups and are hence termed amboceptors. 

 One of these is an ordinary haptophoric group which anchors the 

 antigen to the cell, while the second combines with the complement 

 of the serum and is hence spoken of as the complementophilic group. 

 A special ergophoric group is not present, the changes which occur 

 subsequent to the union between antigen and antibody being 

 effected by the complement of the serum. To this order belong 

 all the cytotoxins (or cytolysins), the immune opsonins, and the 

 lipoidophilic antibody of Wassermann. 



From the above survey it is quite evident that Ehrlich's side- 

 chain theory lends itself exceedingly well to experimental investi- 

 gation, and it may not be out of place to consider in some detail 

 how far the experimental facts support some of the more immediate 

 conclusions to which the theory would lead. 



We have seen that according to Ehrlich, the antibodies are not 

 formed de now, but that they are molecular groups which were once 

 part and parcel of the cell upon which the corresponding antigen has 

 acted. In that case it should be possible to neutralize the effect of 

 the antigen by treating this with the cells from which the antibody 

 is supposedly derived, and conversely we should expect that an 

 admixture of other cells would not produce this result. Ransom 

 was one of the first to investigate this point. After poisoning pigeons 

 with tetanus toxin he found that extracts of all the organs were toxic, 

 excepting those made from the central nervous system. This would 

 suggest that the latter alone had been able to bind the toxin. Wasser- 

 mann and Takaki then showed that this is actually the case, for on 

 rubbing up the same toxin with the brain substance of guinea-pigs, 

 and injecting the mixture into animals, no deleterious results were 

 observed, while the liver, spleen, adrenal glands, muscles, etc., did 

 not have this effect. These results are thus quite in accord with what 

 we would expect on the basis of Ehrlich's theory. 



By working with animals, on the other hand, which are either not 

 at all or but very slightly susceptible to the action of the toxin in 

 question, such as the turtle, the frog, or the alligator, we should expect 

 that the brain substance of these would have little if any neutral- 

 izing action upon the poison. With this supposition the facts are in 

 perfect accord. Analogous results have been obtained by Kempner 

 with the botulismus toxin, which, like the tetanus toxin, possesses 



