DOSAGE 275 



4. Into a healthy horse (previously tested with mallein and tuber- 

 culin) inject either (a) a very small dose of strong tetanus toxin (this 

 method is now little used); (6) a small dose of an attenuated toxin 

 (attenuated with IC1 3 , iodide trichloride); (c) a toxin-antitoxin mixture 

 which is not completely neutralized, but contains a small excess of 

 toxin; (d) first antitoxin and after eighteen to twenty-four hours, toxin. 



5. Repeat injections of toxin at intervals of a few days and increase 

 the doses. 



6. Draw a small amount of blood from the jugular vein and test 

 the antitoxic value of the serum on guinea-pigs and mice. 



7. After two to three months or longer, when the antitoxic value of 

 the serum is found to be high, draw off (ten to fourteen days after 

 last injection) several thousand cubic centimeters of blood under the 

 strictest aseptic precautions. Collect it in sterile vessels and allow it 

 to coagulate in the refrigerator. Separate the serum from the clot 

 and add, as a preservative, 0.5 per cent, carbolic acid or 0.4 per cent, 

 tricresol. Distribute into small dark bottles and keep in a cool, dark 

 place. 



Dosage. A good tetanus antitoxin is used in the following doses: 

 Immunizing or preventive dose 10 to 20 c.c. for a horse; for a 

 smaller animal, 5 to 10 c.c. The passive immunity conferred upon 

 an animal is soon lost. Hence, when a wound in a horse, made 

 accidentally or by operative procedure, does not heal very promptly, 

 it is well to give a second immunizing injection ten days after the first. 

 A unit of tetanus antitoxin is approximately ten times as large as a 

 unit of diphtheria antitoxin. 1 



One unit of tetanus antitoxin is defined as the amount of antitoxin 

 required to neutralize the effects of 1000 times the minimum dose of 

 tetanus toxin fatal to a guinea-pig of 350 grams. If the guinea-pig is 

 protected from death during the first four days after the injection of 

 the toxin-antitoxin mixture, which must have been prepared fifteen 

 minutes before the injection, the dose of antitoxin is called one unit 

 of tetanus antitoxin. 



The United States Government has adopted this unit of tetanus 

 antitoxin and provides those who manufacture antitoxin with a 

 standardized strong tetanus toxin. The German standard unit of 

 tetanus antitoxin is that amount which will neutralize the amount of 

 a standard toxin necessary to destroy 40,000,000 grams of mouse. 

 The French standard is expressed by indicating the weight of anti- 

 toxic serum necessary to protect one gram of mouse against a mini- 

 mum fatal dose of a standard strong toxin. If one-thousandth of a 

 gram (0.001) is necessary to protect a mouse weighing 10 grams, one 

 ten-thousandth of a gram will protect one gram of mouse weight; hence, 

 such an antitoxic serum would be called a 1 to 10,000 antitoxic serum. 



1 One unit of diphtheria antitoxin is that dose which will protect a guinea-pig of 250 grams 

 against the subcutaneous injection of 100 times the minimum fatal dose of a strong, fresh, 

 diphtheria toxin, so that the guinea-pig lives at least four days, but will die after four days. 



