126 Immunity 



toxins, but may not be discovered if there are none. The combina- 

 tion of the toxin-haptophores with the cell-haptophiles can be 

 demonstrated in the test-tube by crushing the cerebral substance of 

 a rabbit, and adding tetanus toxin. The toxin becomes fixed by 

 combination with the cell haptophiles or receptors, loses its further 

 combining powers and fails to affect animals into which it is sub- 

 sequently injected. The increased formation of receptors in con- 

 sequence of repeated stimulation has been shown by the effect of 

 abrin upon the conjunctiva. If dropped into one eye until the 

 conjunctiva is thoroughly immune against its action, the cells of 

 this eye develop a greatly increased capacity for absorbing i.e., 

 fixing the abrin as compared with those of the other eye. Thus if 

 the two conjunctival membranes be dissected out and a certain 

 quantity of abrin triturated with each, the haptophiles of the cells 

 of the immunized membrane fix the poison so that it is no longer able 

 deleteriously to affect animals, while no such effect takes place with 

 the other membrane. 



The ability to stimulate the formation of antibodies is entirely 

 independent of any toxic action and is entirely the work of the hap- 

 tophiles. This is best shown in the fact that diphtheria toxin that 

 has been heated or otherwise manipulated until its toxic action is 

 lost, still retains the power of combining with antitoxin, or of 

 producing antibodies. 



The cells furnishing the haptophile groups or receptors whose 

 presence in the blood gives it its antitoxic quality vary in number or 

 quality in different animals. Thus, in the warm-blooded animals 

 the rapidity with which tetanus toxin is anchored to the cells of 

 the central nervous system seems to indicate that those cells, if 

 not the only cells in the body passing the adapted receptors by 

 which it is anchored, are the chief cells by which it is absorbed. 

 In the alligator, however, other cells seem to fix the toxin before it 

 reaches or connects with those of the nervous system, so that the 

 alligator, though immune against the action of the toxin, is able to 

 make antitoxin as well as susceptible animals. 



Each introduction of appropriate antibody forming substance 

 is followed by an outpouring of the antibody far in excess of what 

 would neutralize it, so that after a systematic treatment has been 

 carried out for some time, the neutralizing value of the blood may be 

 a thousand times what would be necessary to neutralize the total 

 quantity of active substance introduced into the animal. 



Each antibody is specific in action, as must be evident from its 

 mode of formation. Should it be found, however, that several active 

 bodies possessed haptophore groups of identical structure, the anti- 

 body formed by any of them might be found to possess common 

 neutralizing powers for all. 



The animal whose blood contains antibodies enjoys immunity 

 from the active body by which they were formed only so long as 



