DIPHTHERIA. 299 



guinea-pig in three days). This period of time covered 

 that of the greatest growth of the bacilli, as shown both 

 by the appearance of the culture and by the number of 

 colonies developing on agar plates." 



"The bodies of the diphtheria bacilli did not at any 

 time contain toxin in considerable amounts." "The 

 type of growth of the bacilli and the rapidity and extent 

 of the production of toxin depended more on the reaction 

 of the bouillon than upon any other single factor." 

 " The best results were obtained in bouillon which, after 

 being neutralized to litmus, had about 7 c.cm. of normal 

 soda solution added to each liter. An excessive amount 

 of either acid or alkali prevented the development of 

 toxin." "Strong toxin was produced in bouillon con- 

 taining peptone ranging from i to 10 per cent." "The 

 strength of toxin averaged greater in the 2 and 4 per 

 cent, peptone solution than in the i per cent." 



"When the stage of acid reaction was brief and the 

 degree of acidity probably slight, strong toxin developed 

 while the culture bouillon was still acid; but when the 

 stage of acid reaction was prolonged little if any toxin 

 was produced until just before the fluid became alka- 

 line." 



"Glucose is deleterious to the growth of the diphtheria 

 bacillus and to the production of toxin when it is present 

 in sufficient amounts to cause by its disintegration too 

 great a degree of acidity in the culture-fluid. When the 

 acid resulting from the decomposition of glucose is neu- 

 tralized by the addition of an alkali the diphtheria 

 bacillus again grows abundantly." 



The Immunization 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, 



