134 PATHOGENIC BACTERIA. 



Martin and Cherry found that the molecular structure 

 of the toxin was changed by admixture with the anti- 

 toxin. They found that under pressure toxin passes 

 freely through a film of gelatin in a Chamberland filter, 

 but that antitoxin does not. If a quantity of toxin equal 

 to eight fatal doses per cubic centimeter is mixed with 

 just enough antitoxin to neutralize it and the mixture 

 allowed to stand for two hours, then filtered through 

 gelatin, as much as 4 c.c, equalling thirty-two fatal 

 doses, can be injected into guinea pigs without ill-effects. 

 If the toxin had not been changed before being subjected 

 to filtration, it should have passed through. 



An interesting paradox of immunity is made use of by 

 Behring to aid in proving the directness of the chemic 

 reaction. It is a fact that when rabbits are immunized 

 to tetanus so as to be resistant to subcutaneous injections 

 of the toxins they die of tetanus when the toxin is in- 

 jected into the brain substance. Behring thinks this to 

 be the result of the impenetrability of the blood-vessels 

 to the antitoxin which does not dialyze. The toxin 

 being injected into the brain substance acts directly 

 upon the nervous system and produces death, although 

 if it had to reach the same tissue by absorption through 

 the lymphatics and circulation in the blood it must 

 suffer neutralization in the latter. If in making the 

 intracerebral injection the vessels are injured so that the 

 blood flows out and comes in contact with the toxin, the 

 animal will recover. Mixtures of toxin and antitoxin 

 when injected into the brain provoke no tetanus. 



2. Theory of Cytic Stimulation. — Buchner, Metschni- 

 koff, Roux, Calmette, and others contend that that which 

 we see in the so-called neutral mixture bears no definite 

 relationship to what goes on in the body, and that the 

 toxin is not neutralized by the antitoxin mixed with it, 

 but destroyed by the cells of the body aroused to energetic 

 action by the stimulating effect of the antitoxin. In 

 support of this view Roux has shown that when so-called 

 neutral mixture of tetanus toxin and antitoxin, incapable 



