DIPHTHERIA. 231 



is added to the cultures, which are then filtered through 

 porcelain. If the toxin must be kept before using, it is 

 best to preserve it unfiltered, as it deteriorates more rap- 

 idly after nitration. Unfiltered toxin causes too much 

 local irritation. If the bacillus employed was virulent 

 and the conditions of culture were favorable, the filtered 

 culture should be so toxic that o. i c.cm. would be fatal to 

 a 5oogram guinea-pig in twenty-four hours (Roux). Even 

 under the most favorable circumstances it is difficult to 

 obtain a toxin which will kill in less than thirty hours. 



The experience of the author with Fernbach's appara- 

 tus has not been satisfactory. The passing current of air 

 is a frequent source of contamination to the culture, and 

 requires great care. In the end it is questionable whether 

 the toxin thus produced is better than that obtained from 

 an ordinary flask exposing a large surface to the air. 



The Immunisation of the Animal. The animals chosen 

 to furnish the antitoxic serum should be animals which 

 present a distinct natural immunity to ordinary doses of 

 the toxin, and should be sufficiently large to furnish large 

 quantities of the finished serum. Behring originally 

 employed dogs and sheep ; Aronson at first preferred the 

 goat ; but Roux introduced the horse, which is more easi- 

 ly immunized than the other animals mentioned, and, 

 being large enough to furnish a considerable quantity 

 of serum, recommends itself strongly for the purpose. 



The animal chosen should be free from tuberculosis 

 and glanders, as tested by tuberculin and mallei n, but 

 need not be expensive. A horse with a disabled foot 

 will answer well. Rheumatic horses should be rejected. 

 In the beginning a small dose of the toxin about i 

 c.cm. should be given hypodermically to detect indi- 

 vidual susceptibility. Horses vary much in this particu- 

 lar, as Roux has pointed out. The author found light- 

 colored horses to be distinctly more susceptible than 

 dark-colored ones. 



If well borne, the preliminary injection is followed in 

 about eight days by a larger dose, in eight days more by 



