38 INFECTION 



If toxin and an ti- toxin (see immunity chapter) are mixed in rela- 

 tive proportions, chemical neutralization takes place. Since the 

 toxins cannot be isolated in a chemically pure form, their exact 

 composition cannot be known, except by studying their effects upon 

 animals and animal tissues. Hence, when anti-toxin, added to 

 toxin in a test-tube is injected into an animal, and no harm results, 

 it is rightly assumed that the toxin is neutralized, and both are 

 chemically bound; yet if fresh toxin is added to the mixture, it is no 

 longer neutral. 



If the toxin of the pyocyaneus and the anti- toxin be mixed so 

 that they neutralize each other, and if the mixture is heated, the 

 neutralization disappears, and the mixture becomes toxic again. 

 That the union is a chemical one, may be inferred from the fact 

 that it is more rapid in concentrated solution than in weak, and is 

 much quicker when warmed than when cold, and it follows the law 

 of multiples, one part toxin neutralizing one part of anti- toxin, and 

 ten parts of toxin neutralizing ten parts of anti-toxin. All this is in 

 accord with chemical laws. Toxins sometimes degenerate into 

 what Ehrlich has called toxoids, substances that bind (unite with) 

 anti- toxin just as effectively as toxins, while they are not poisonous, 

 yet may stimulate healthy cells to secrete anti-toxins if they are 

 injected into the body of experiment animals. 



More is known about the toxins of diphtheria and tetanus bacilli 

 than of any other. Diphtheria toxin has numerous component sub- 

 stances, one of which is the toxin that causes the acute phenomena 

 of diphtheria intoxication. Another, toxon, causes cachexia and 

 paralysis some time after infection. 



Tetanus toxin is composed of two substances; tetanospasmin and 

 tetanolysin. The first unites chemically with the motor elements 

 of the nervous system, producing degeneration and causing tremen- 

 dous contractions of the muscles governed by the nerves involved. 

 The second has the property of dissolving tissues, such as blood cells. 



Tetanus toxin travels from the infected site to the cord by way of 

 the nerves; it is exceedingly poisonous; a single prick of the finger 



