298 



Society Proceedings (122). 



pepsin the M.L.D. of toxin is reduced to that of the original 

 filtrate (M.L.D. = 3 X io~ 7 c.c.), but no further reduction of 

 toxicity could be observed during further incubation for 48 hours. 



That the reduction of toxicity is not due to peptic digestion 

 follows from the fact that toxicity was only partly destroyed and 

 in fact was reduced exactly to the level at which it existed in the 

 crude toxin. Besides, identical reduction of potency was ob- 

 served when heated (8o° C.) pepsin was added to the acid toxin. 

 Neither could the reduction of toxicity be ascribed to spontaneous 

 deterioration of toxin, since the control mixture consisting of 

 toxin and acid buffer alone maintained its high toxicity to the 

 end of the experiment (48 hours). On the other hand the failure 

 of pepsin to completely digest the toxin is not due to the possible 

 presence in the toxin of some inhibiting substance, since the 

 activity of pepsin against edestin in the controls proceeded equally 

 well in the presence as in the absence ol the culture filtrate of 

 B. botulinus. 



Thus the reduction of potency of the acidified toxin in the 

 presence of pepsin is not due to its digestion, but most likely to 

 some physical phenomenon such as ready adsorption (?), which 

 possibly returns the particles of toxin from the state of high degree 

 of dissociation to the more stable state where they exist in a 

 condition of undissociated aggregates. 



II. As we have previously stated 1 the crude toxic filtrate of the 

 culture of B. botulinus killing mice by the intraperitoneal injection 

 in the amount of 3 X io~ 7 c.c. can be rendered so potent by acidifi- 

 cation that it will kill mice in the dose of 3 X io~ 18 c.c. However, 

 if this crude filtrate is salted out with (NH 4 ) 2 S0 4 , the precipitate 

 which contains all of the original toxin in a concentrated state 

 can no longer be rendered more potent by acidification. 



If the tentative assumption that the toxicity of botulinus toxin 

 may depend on the degree of dispersion of its particles is correct, 

 and if in the original toxin the coarser aggregates may be dis- 

 persed by acidification, it seems that precipitation with ammonium 

 sulphate renders the particles uncapable of dispersion. 



III. If the changes in the structure of botulinus toxin, brought 

 about by the adjustment of its hydrogen-ion concentration are of 

 the nature of an increase of dispersion of its particles, one might 



