THE DIPHTHERIA BACILLUS 305 



toxicity very materially. An exposure to 60 C. for ten hours, or at 

 70 C. for two hours, attenuates the toxin, and it is rapidly inactivated 

 or destroyed at 100 C. 



Protein precipitants, as ammonium sulphate and alcohol, precipitate 

 the toxin from the broth in an insoluble state with but little reduction 

 in potency. The precipitate, after dialysis to remove the salts, is 

 soluble in water. A further reduction in volume and partial puri- 

 fication can be attained by evaporating the broth to one-tenth its 

 original volume in vacuo at a temperature not exceeding 25 C. (in 

 the dark), precipitating with alcohol, filtering and dissolving in water, 

 and again precipitating, then drying the precipitate in vacuo. 



Physiological Action. The chemical constitution of the toxin mole- 

 cule is unknown, and toxin can not be detected or assayed chemically. 

 It provokes, however, a definite physiological response in susceptible 

 animals, as guinea-pigs, and its presence is detected and its strength 

 determined by injecting graduated doses into them, as mentioned above. 

 From its physiological action the toxin molecule appears to consist 

 of three components in varying amounts: (a) Toxin, which causes 

 the acute symptoms of intoxication, parenchymatous degeneration 

 and death when injected into susceptible animals. This fraction of 

 the toxin, according to Ehrlich, has a special affinity for the antitoxin. 

 (b) Toxone: the toxone causes edema at the site of inoculation and 

 the postdiphtheritic paralyses. It combines with antitoxin more 

 slowly than the toxin, (c) Toxoid: diphtheria toxin rather readily 

 loses its toxic properties on standing, retaining its power of com- 

 bining with antitoxin unimpaired, however. Toxin which is devoid 

 of toxic power but which combines with antitoxin is called "toxoid." 



Antitoxin. Preparation. The injection of the soluble toxin of the 

 diphtheria bacillus in sublethal doses into experimental animals stimu- 

 lates the formation of specific antitoxin which has both curative and 

 prophylactic value. Antitoxin is obtained from horses because they 

 are less susceptible to the action of the toxin than smaller animals. 

 The serum of horses, at least in single doses, is innocuous for man, and 

 horses furnish large amounts of blood (containing antitoxin) without 

 injury to the animal. Young animals free from glanders, tuberculosis 

 and other diseases are used for the purpose. Several methods are 

 available for immunization, but the one commonly selected is carried 

 out in the following manner: an initial injection of diphtheria toxin, 

 either mixed with an excess of antitoxin or attenuated by iodin 

 trichloride, is made and about a week later a second injection con- 



