DIPHTHERIA. 



219 



The following instance, taken from the text-book of 

 Mace, will illustrate the immunization of a horse by the 

 method of Roux. For the better comprehension of the 

 description it should be mentioned, as has already been 

 pointed out in the consideration of the physiology of the 

 disease (p. 211 ), that the toxin is the equivalent of the fil- 

 trate of a bouillon-culture, or of a culture in which the 

 bacilli have been destroyed by addition of carbolic acid in 

 a proportion of o. 5 per cent. : 



No reaction. 



Slight edema, without fever. 



Marked edema, disappearing 

 in the course of twenty- 

 four hours. 



Small doses of pure toxin may also be employed in the 

 first inoculations. Some horses bear from the beginning 

 I cu. cm. of a toxin of which -^ cu. cm. is sufficient to 

 destroy within forty-eight hours a guinea-pig weighing 

 300 grams. The immunity can be looked upon as well 

 established after the animal has received from 60 to 70 cu. 

 cm. of this toxin. It is then possible to inject much larger 

 amounts without injury. In order to obtain diphtheria- 

 antitoxin it is best to employ horses, in the first place be- 

 cause they are very readily immunized, and in the second 

 place because they can be bled innumerable times. 



In immunizing the animals a normal toxin-solution must 

 be available to begin with, and which affords a standard of 

 comparison. Behring designates as a diphtheria normal 

 toxin that diphtheria-solution of which I cu. cm. represents 

 the minimal lethal dose for 100 guinea-pigs each weighing 

 250 grams. To indicate this normal toxin, he has intro- 



