THE ORIGIN OF ANTITOXIN THE SIDE-CHAIN THEORY 107 



sions of the brain must remain in contact with the toxin for some 

 time before the latter is neutralized. 



It was urged by many writers that the brain cannot be the site 

 of production of antitoxin, since the injection of tetanus toxin 

 direct into the brain of immunized animals causes the develop- 

 ment of tetanic symptoms. This argument is obviously fallacious. 

 A cell that is secreting antitoxin still possesses side-chains suitable 

 for union with the toxin ; it possesses them, indeed, in increased 

 amount, and is therefore, if anything, more susceptible to the 

 action of the toxin. The antitoxin which is circulating in the 

 blood only prevents the toxin from reaching the cell, acting much 

 in the same way as a lightning conductor. 



Further research, however, seems to prove definitely that the 

 neutralizing properties of brain substance are not due to the 

 presence of a substance having any real likeness to antitoxin. 

 Thus, Metchnikoff showed that when an emulsion of frog's brain 

 is mixed with tetanus toxin no neutralization takes place, although 

 the frog is, under certain circumstances, susceptible to the action 

 of the toxin ; these researches were corroborated by Courmont 

 and Doyon. Arguing from this and other facts, Metchnikoff 

 attributed the fixation fo tetanus -as*itoxin by the central nervous 

 system to the presence in the latter of fatty substances ; these are 

 absent from the brain of the frog. In support of this view, several 

 observers found that substances such as lecithin, cholesterin, 

 tyrosin, etc., have also the power of neutralizing various toxins. 



It was objected to these researches of Metchnikoff and Cour- 

 mont and Doyon that these experimenters did not leave the 

 tetanus toxin in contact with the brain substance for a sufficiently 

 long time. But this seems unnecessary, since the emulsion of the 

 central nervous system of higher animals will neutralize tetanus 

 toxin if the mixture be injected immediately, or even if the 

 two substances are injected separately, though in this case the 

 necessary amount of brain substance is larger. And Danysz 

 showed that if a neutral mixture of brain and toxin be macerated 

 for a long time in salt solution the toxin is again set free, in which 

 again the phenomenon is unlike that presented by antitoxin in its 

 action on toxin. 



The researches of Morax and Marie also point in the same 

 direction. They showed that the fixative power of the brain is 

 almost entirely destroyed by drying, whereas, as we know, that 

 process has practically no effect on antitoxin. The researches of 



