^OB l.OCAL riSSUE REACTIVITY 



tiic ])licn()incii()ii possess a considciable Ileal lesistaiue. The heat 

 resistance may clifter, however, with various niicroorganisms and 

 even strains of the same microorganism. It may also be influenced 

 by the mode of preparation of the active material (i.e., amomit of 

 autolysis, medium ingredients, etc.) . 



In view of the variations in the heat resistance of true exotoxins, 

 and also in view of the fact that different factors may influence 

 the heat resistance of the active principles, the use of this test for 

 purposes of classification carries little conviction. 



Strains of B. diphlheriae differ \videly in toxigenicity. Many 

 workers encountered strains producing weak toxins. Some strains, 

 however, possess high toxigenicity which may remain unaltered 

 for many years. The best example is strain Park-Williams No. 8, 

 which is iniiversally used for tlie production of diphtheria toxin. 

 B. diplithcruw strains may lose their toxigenicity (variations in 

 peptones, concentration of iron, Pappenheimer and Johnson, 

 1936, etc.) . 



The skin-preparatory and reacting factors of the phenomenon 

 fluctuate in potency in the same iiltrate. On many occasions there 

 \vas observed a gradual decrease in the potency as well as com- 

 plete inactivation of the filtrates stored in the refrigerator for 

 several months. Various strains of the same microorganism differ 

 widely in their ability to produce active principles. One strain 

 of meningococcus 44B. maintained in the laboratory for several 

 years gave rise to active principles, potent in dilution of 1:4000. 

 After its preservation on egg medium the ability to produce 

 active principles ^vas completely lost and could ne\'er be restored 

 in this strain in spite of persistent passages through favorable 

 media. A strain of B. typhosus Tl, successfully employed for prep- 

 aration of active principles for a period of eight years, for 

 unknown reasons lost its power to produce the principles. Wide 

 differences in the potency of different strains belonging to the 

 same serological group have been noted in this laboratory and by 

 various investigators in connection ^vith meningococcus. 



No relation exists between virulence and toxigenicity of B. 

 dipJitJieriae. The virulence is lost by passage through artificial 

 media whilst toxigenicity may persist. On the other hand, whilst 

 the virulence may be restored by animal passage strains which 

 lose toxigenicity do not regain it in the animal (Walbum) . Of spe- 

 cial interest in this connection are the investigations of Anderson, 

 Happold, McCleod and Thomson (1931) , who differentiated three 



