DIPHTHERIA ANTITOXIN 87 



to form a surface growth. It is at the surface that the toxin function is most marked, 

 hence in growing diphtheria for toxin formation we use Fernbach flasks which expose 

 a large surface to the air. It is a marked acid producer bouillon with a + 1 reaction 

 becoming +2.5 to +3 in thirty-six hours. The filtrate from a two- or three- weeks- 

 old broth culture is highly toxic, and is usually referred to as diphtheria toxin. It 

 is used in injecting horses to produce antitoxin. Ehrlich uses as a standard to meas- 

 ure the toxicity of toxin the minimal lethal dose (M. L. D.). This is the amount 

 of toxin which will kill a 35o-gram guinea-pig in just four days. Some toxins have 

 been produced whose M. L. D. was 1/500 c.c., so that i c.c. of such toxin would kill 

 500 guinea-pigs. Theoretically, the measure of an antitoxin unit is the capacity 

 of neutralizing 200 units of a pure toxin. (On exposure to light, etc., toxin loses 



FIG. 27. Diphtheria bacilli involution forms. (Kolle and Wassermann.) 



its toxic power and is termed toxoid.) Inasmuch, however, as toxoneand toxoid 

 are also present, we may practically consider an antitoxin, or immunizing unit 

 (i.e., Immunitatseinheit) as about capable of making innocuous 100 M. L. D. 



In the preparation of antitoxin horses are employed; the method being to inject 

 the bouillon filtrate or toxin subcutaneously at weekly intervals for a period of three 

 or four months. When each c.c. of the serum of the horse is found to contain about 

 250 to 500 antitoxin units the horse is bled from the jugular vein. Some sera contain 

 as much as 1300 units in a cubic centimeter. 



Methods of purifying and concentrating antitoxin are now employed by certain 

 makers, the principle being that the antitoxin in the horse serum is precipitated 

 with the globulins which come down on half saturation with ammonium suplhate. 

 In this way, as the content in horse serum proteids is lessened, the anaphylactic 

 dangers are lessened. 



As a curative measure, from 2500 to 5000 units should be injected. 

 If the injection is delayed or the case very serious the dose should be 

 10,000 units. As much as 50,000 units has been given in severe cases. 

 The prophylactic dose is 500 units. 



