Botulinus toxin resists a degree of acidity equivalent to that of the stomach even when exposed thereto for 24 hours at 37°C. It is less resistant to alkali, however, as shown by the fact that in a medium of weakly alkaline reaction its potency is reduced to less than one-tenth in 24 hours. It is unaffected by peptic and tryptic digestion. Because of its instability in mildly alkaline solutions and resistance to acid, there is reason to believe that the toxin is in the main absorbed from the upper portion of the digestive tract; that is to say, from the stomach and upper duodenum.

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