50 ADAPTATION AND DISEASE 



elaborated in excess, a body substance which neutralizes the 

 toxin, and what is more, once started they continue for weeks 

 and months to elaborate the " antibody." 1 



As to how these antitoxins are produced : it used to be 

 thought that there was a direct conversion of toxin into anti- 

 toxin. But this cannot be. Kroon 2 has shown that in the 

 horse a single toxin unit (of tetanus) can lead in the process of 

 immunization to the production of 1,000,000 antitoxin units. 3 

 Toxins, it is true, may have some such function in the first place, 

 but later it is the cells themselves which assimilate the necessary 

 constituents and build up and discharge the antitoxins. 



For this also has been clearly determined namely, that it 

 is the cells that take up and fix the toxins which produce the 

 antitoxins. Ehrlich it was who drew the important distinction 

 between those substances which simply diffuse into the cell 

 and those which diffusing become fixed in the cell, calling atten- 

 tion to the fact that antibodies are not formed against members 

 of the former group, against, for example, alkaloids. The 

 members of this group disappear from the blood, but by alcohol 

 and other extractives they can be removed from the tissues. 

 This is not true with regard to the second group, or, more accur- 

 ately, substances of this second order may be extracted from 

 certain tissues but not from others, and it is the latter apparently 

 which, fixing the toxin, produce the antitoxin. The conjunctiva 

 ordinarily is most sensitive to abrin, which sets up a violent 

 conjunctivitis, but if this be administered locally in minute 

 but progressively increasing amounts, the conjunctiva can be 

 rendered insensitive or immune to this phytotoxin. Homer 4 

 rendered the conjunctiva of one eye in the rabbit insensitive to 

 abrin, killed the animal, and now triturated the conjunctiva of 

 each eye with a poisonous dose of abrin. The animal inoculated 

 with the mixture from the untreated eye died, that inoculated 

 with the preparation of the immunized eye survived, or other- 

 wise there was clearly a local production of antitoxin by the 



1 Let me admit that this is a barbarous hybrid. There is, however, a certain 

 felicity about it, considering that it is a provisional word which should dis- 

 appear when we know, as we do not know at present, the exact chemical or 

 physical nature of this class of substances. 



* Mftnchener med. Wochenschr., 1898, 321 and 362. 



3 See also McFarland, Textbook of Bacteriology, 3rd ed. 



* Archivf. Ophthalmologie, lii., 1901, 72. 



