420 DIPHTHERIA 



formation, provided that a considerable amount of peptone, 2 per 

 cent., be added, and the medium be made sufficiently alkaline ; 

 after making it neutral to litmus they add to each litre of broth 

 7 c.c. of normal caustic soda solution. There is in all cases a 

 period at which the toxicity reaches a maximum ; Roux and 

 Yersin found this period to be two to three weeks, but later 

 observers find that in favourable conditions the greatest toxicity 

 is reached about the tenth to twelfth day, sometimes even 

 earlier. It may be added that the power of toxin formation 

 varies much in different races of the diphtheria bacillus, and 

 that many may require to be tested ere one suitable is 

 obtained. 



Properties and Nature of the Toxin. The toxic substance in 

 filtered cultures is a relatively unstable body. When kept in 

 sealed tubes in the absence of light, it may preserve its powers 

 little altered for several months, but, on the other hand, it 

 gradually loses them when exposed to the action of light and 

 air. As will be shown later (p. 564), the toxin probably does 

 not become destroyed, but its toxophorous group suffers a sort of 

 deterioration, so that a toxoid is formed which has still the 

 power of combining with antitoxins. Heating at 58 C. for 

 two hours destroys the toxic properties in great part, but not 

 altogether. When, however, the toxin is evaporated to dryness, 

 it has much greater resistance to heat. One striking fact, 

 discovered by Roux and Yersin, is that after an organic acid, 

 such as tartaric acid, is added to the toxin the toxic property 

 disappears, but it can be in great part restored by again 

 making the fluid alkaline. 



Guinochet found that toxin was formed by the bacilli when 

 grown in urine with no proteid bodies present. After growth 

 had taken place he could not detect proteid bodies in the fluid, 

 but, on account of the very minute amount of toxin present, 

 their absence could not be excluded. Uschinsky also found that 

 toxic bodies were produced by diphtheria bacilli when grown in 

 a proteid-free medium. 1 It follows from this that if the toxin 

 is a proteid, it may be formed by synthesis within the bodies of 

 the bacilli. Brieger and Boer have separated from diphtheria 

 cultures a toxic body which gives no proteid reaction (vide p. 

 199), Whether or not diphtheria toxin is of proteid nature 

 must, however, be considered to be a question not yet settled. 1 



1 Uschinsky's medium has the following composition : water, 1000 parts ; 

 glycerin, 30-40 ; sodium chloride, 5-7 ; calcium chloride, - 1 ; magnesium 

 sulphate, -2-'4 ; di-potassium phosphate, '2-'25 ; ammonium lactate, 6-7 ; 

 sodium asparaginate, 3-4. 



