102 THE ACUTE SELF-LIMITED INFECTIONS 



Diphtheria Antitoxin. The specific poison of the organisms 

 and the means used to neutralize it must now be discussed. 

 The poison of the diphtheria bacillus is not only made in 

 the false membrane in the human case, but is elaborated by 

 the organism in artificial media in a laboratory. This poison 

 itself will kill the lower animals. The toxin is obtained by 

 growing the germs on broth, made in a manner found most 

 suitable for its development. The broth is freed of bacterial 

 bodies and injected into horses. This animal is chosen for 

 its size and freedom from disease affecting humans, and 

 because large quantities of material may be injected and 

 much blood withdrawn without harming the beast. The 

 horses receive under the skin gradually increasing amounts 

 of this toxic broth until they are able to withstand huge 

 quantities, many times the dose necessary to kill them if 

 given at first. They are then considered to have some neu- 

 tralizing substances for this toxin. This neutralizing property 

 is known to be in the blood serum. The horse is then bled, 

 and the serum separated from the red blood cells. It is 

 tested against the original toxin used for making the injec- 

 tions. This is done by mixing the two in definite parts, 

 allowing the mixture to stand a few minutes, and injecting 

 it into guinea-pigs. By appropriate technic the number of 

 "units" is determined. A "unit" is that quantity of horse 

 serum, or antitoxin, which will neutralize 100 times the 

 smallest quantity of toxin necessary to kill a guinea-pig 

 weighing 250 grams (8 ounces) . 



The horse-serum antitoxin has now a value for clinical 

 purposes, as the quantity to be given can be controlled. 

 Newer methods have permitted the refinement and concen- 

 tration of this antitoxin, so that there is now less incon- 

 venience in giving it. The dose for treatment varies from 

 1500 to 20,000 units by injection under the skin depending 

 upon the severity of the case; in bulk this may be less than a 

 teaspoonful. In very severe or malignant diphtheria the 

 best results are obtained by giving the antitoxin into a vein. 



