Bacilli of diphtheria 



SnMll quantities 

 ,. Heated Filtered to 0^"Q> inje<Ked under skin 



growing in a broth /^tokili bacteria separate toxin of healthy horse 



Doses repeated daily - increasing amounts for several weeks 



Blood drained 

 ^*>^ ^from large vein 

 in horse's 

 neck 



Blood Serum 



clots ^ containing 



// antitoxin 

 Serum 

 tested on 



Sterilized 

 ed 



Divided into doses, 

 or units, of antitoxin 



guinea pigs 



PREPARING DIPHTHERIA ANTITOXIN 



For making antitoxins, carefully selected and perfectly healthy young animals are 

 used. The toxin is produced by millions of bacteria grown in special nutritive solu- 

 tions. The dissolved poison is filtered from other substances in the culture, which is 

 heated to kill the bacteria. Increasing doses of toxin are injected into the animal 

 over two to three months. Blood is drawn from the animal from time to time; after 

 the blood clots, the antitoxin is in the serum. After the removal of other materials 

 the serum is tested both for its potency and for the possibility of any injurious sub- 

 stance being in it. It is then put up in sealed units for use against diphtheria 



be used to cure a person infected with the corresponding disease germs. 

 That is, the antitoxin produced in the body of a horse or a goat is used to 

 reinforce the natural capacity of the human body to combat the poison of 

 the invading germs (see illustration above). 



Are Chemical Changes in an Organism Permanent? 



Modified Protoplasm If the body recovers from a mechanical injury, 

 it may afterward be exactly as it was before, for all we can tell — except 

 perhaps for some mutilation. But when a person recovers from certain 

 kinds of sickness, there are apparently lasting changes in the protoplasm. It 



234 



