410 BACTERIOLOGY. 



DIPHTHERIA ANTITOXIN. As stated above, the 

 growth of bacterium diphtheria? is accompanied by the 

 elaboration of a poison of remarkable toxicity that is 

 accountable for the constitutional symptoms and patho- 

 logical lesions by which the disease is characterized. If 

 by appropriate methods this poison (toxin) be separated 

 from the bacteria by which it was formed, it is capable, 

 when injected into susceptible animals, of causing death 

 and practically all the lesions that accompany the dis- 

 ease when due to the invasion of the living bacteria. If, 

 on the contrary, the dose of poison be so adjusted as to 

 cause only temporary inconvenience and not endanger 

 life, and this dose be injected repeatedly, gradually in- 

 creasing in size as the animal is able to bear it, after a 

 while a marked tolerance is established, so that the animal 

 may be given many times the amount of the toxin that 

 would otherwise prove fatal /. e., many times the lethal 

 dose for an animal that had not acquired such a tolerance. 



If blood be now drawn from the animal that has 

 become habituated, so to speak, to the diphtheria toxin, 

 and the serum collected from it, we discover several 

 important facts, viz. : 



That this serum when mixed with the previously 

 determined lethal dose of the toxin in a test-tube will 

 either neutralize its toxicity or greatly reduce it, accord- 

 ing to the amount of serum used. 



That if we inject into an animal the determined fatal 

 dose of the toxin, and immediately afterward inject a 

 quantity of the serum, either the animal will not die or 

 the death will be more or less delayed, according to the 

 amount of serum employed. 



That if a susceptible animal be inoculated with a 

 living culture of virulent bacterium diphtherise, its life 



