MICROORGANISMS AND HUMAN WELFARE 35 



31. Treatment of diphtheria. But these germs do not 

 have things all their own way. The cells of the body seem 

 to know when an army of this enemy has entered their terri- 

 tory, and they at once set to work to produce substances 

 that will neutralize or overcome the toxins formed by the 

 diphtheria bacteria; these substances are known as anti- 

 toxins. When the disease is at its height, there is a fierce 

 battle between the invading microbes with their toxins and 

 the cells of the body fighting for their lives by means of 

 their antitoxins. If the bacteria are victorious, death ensues. 



In the year 1892 a most important discovery was made by 

 a German bacteriologist named Von Behring. He found 

 that it is not necessary for the human body to manufacture 

 all the antitoxin it needs for its struggle with the diphtheria 

 poisons, but that this substance may be taken from the blood 

 of other animals that have produced it. For this purpose, 

 healthy horses are now secured by city boards of health, and 

 a small dose of diphtheria toxin is injected into their bodies: 

 the next day a larger dose may be given with little or no ill 

 effects ; until, at the end of several months of this treatment, 

 the animals can stand a quantity of the poison that would 

 have proved fatal if given at an earlier time. For during 

 all these days the horse has been having a very mild form 

 of diphtheria, and the cells of his body have been producing 

 and giving into the blood an amount of antitoxin much more 

 than is needed to neutralize the diphtheria poisons the ani- 

 mal has received. Some of the blood is then carefully re- 

 moved and allowed to clot. The liquid serum that oozes 

 out of the clot contains the antitoxin, which is carefully 

 prepared for injection into the body of human beings when 

 diphtheria attacks them. And so our good friend the horse, 

 without any permanent ill-effects to himself, has decreased the 

 death rate formerly caused by diphtheria by 75 to 80 per cent. 



