SERUM THERAPY 93 



Testing the Serum for Strength. A standard of strength 

 for antitoxin is established by the government, which 

 provides the manufacturing laboratories with small 

 quantities of test antitoxin for determining the test dose 

 of toxin with which to test the antitoxin manufactured. 

 The amount of test toxin which when mixed with one 

 unit of the test antitoxin furnished by the government 

 will kill a guinea-pig weighing 250 grams in just four days 

 is termed the test dose of toxin. The smallest amount 

 of serum which will save or prolong a 25o-gram pig's life 

 just four days when injected with the test dose of toxin 

 will, therefore, be said to contain a unit of antitoxin. 

 If, therefore, it requires ^75- c.c. of serum to save the 

 pig's life for four days, the serum will contain 400 units 

 of antitoxin per cubic centimeter. After the strength 

 of the serum has been determined, a small amount of 

 trikresol, a harmless antiseptic, is added to prevent 

 contamination in handling the serum after it leaves the 

 laboratory, and the serum is tested for sterility. 



Testing for Bacteria. A small quantity of the serum 

 is mixed with an equal quantity of sterile bouillon and 

 placed in an incubator, where it is kept for five days, 

 when it is examined microscopically and a portion in- 

 jected into a guinea-pig, which is watched for several 

 days for symptoms of infection of any kind. Should 

 it not be found sterile, the entire lot is rejected. 



Antidiphtheric Globulins or Concentrated Antitoxins. 

 It has been determined that the real antibodies of the 



