SPECIAL PROPERTIES OF THE PRINCIPAL TOXINS 115 



Diphtheria toxins have been classified into three groups, depending 

 upon the degree of avidity for antitoxin they display, viz., prototoxin, 

 deuterotoxin, and tritotoxin. Each of these toxin groups may, in 

 whole or in part, be converted into toxoids. The prototoxin has a 

 greater affinity for the antitoxin than has the deuterotoxin, and the 

 deuterotoxin has a greater affinity for the antitoxin than has the trito- 

 toxin. The same relation is apparent with the three toxoids, which are 

 not poisonous, but which have the same power of combining with 

 antitoxin as have the toxins from which they take their origin. 



In standardizing antitoxin, it is found in general that with a perfectly 

 fresh toxin a certain amount of antitoxin will just neutralize a definite 

 amount of toxin. If older toxin is used, it is found that the toxin has 

 lost about one-half its toxic power, but retains its initial power for 

 neutralizing antitoxin. Ehrlich explained this by showing that the 

 diphtheria toxin molecule is composed of two groups one the carrier 

 of the toxic qualities, the toxophore group, which is quite labile; the 

 other uniting the whole molecule with antitoxin, being capable of neu- 

 tralizing it, and characterized by its stability. The toxophore group 

 being destroyed as in old toxin, the poison loses its toxic qualities, but 

 retains its power to bind antitoxin. This modified toxin or non-poisonous 

 diphtheria toxin has been designated by Ehrlich "diphtheria toxoid." 



2. Tetanus Toxin. Of all bacteria classed as true toxin producers, 

 none possesses greater toxicity than does the tetanus bacillus. The 

 number of organisms producing sufficient toxin to cause a fatal infection 

 may be so small that careful anaerobic cultures made from the local 

 lesion of infection, together with injection of the wound secretions into 

 white mice, may fail to disclose the presence of tetanus bacilli. 



According to Ehrlich, tetanus toxin is composed of two separate and 

 distinct substances (1) Tetanospasmin, a neurotoxin, which is very 

 labile and responsible for the severe symptoms of the infection; (2) 

 tetanolysin, a hemotoxin, which is more stable and destructive for er^ 

 throcytes. 



Tetanus toxin is prepared by cultivating the bacillus in bouillon 

 under strict anaerobic conditions. Since tetanospasmin is so suscep- 

 tible to the influence of heat, age, and even light, the toxin is best pre- 

 served in a dry form. The standard of tetanus toxin consists of 100 

 minimal lethal doses of a precipitated and dried toxin, preserved at the 

 Hygienic Laboratory of the Public Health and Marine-Hospital Service. 



If susceptible animals, such as mice or guinea-pigs, are injected sub- 

 cutaneously or intravenously with tetanus toxin, they begin to manifest 



