ANTITOXINS AND RELATED ANTIBODIES 



137 



each liter. In some cases it is filtered through a porcelain filter, 

 which will remove the bodies of the bacteria, but not the soluble 

 toxins. The amount of toxin present in the solution must be 

 next determined for two reasons: first, to insure the presence of 

 toxins in sufficient concentration for efficient immunization, and, 

 second, to determine the amount that may be injected into the 

 horse without serious injury. The amount of toxin that, when 

 injected subcutaneously, will kill a guinea-pig weighing 250 gm. 

 in three days is called the minimum lethal dose for the guinea-pig 

 (abbreviated M. L. D.). The broth should contain at least 1000 



Fig. 66. Apparatus for the injection of considerable quantities of toxin 

 into the horse: a, Graduated cylinder closed by a rubber cork, b. Air is 

 pumped into the constant pressure bulb e, and from this passes into the cylinder. 

 The toxin is forced out through the needle at i (Levaditi). 



M. L. D. per cubic centimeter. The horse is most commonly 

 employed for the production of the antitoxin. Care is used that 

 the animal is fairly vigorous and entirely free from any infectious 

 disease. Injections of 100 M. L. D. are made subcutaneously, 

 or, better yet, larger amounts, neutralized by antitoxin already 

 prepared, are first used. The animal responds by fever and 

 swelling at point of injection and by other minor symptoms. 

 After a lapse of several days, or when the horse has recovered, a 



