Both of these toxins are not extractable by the conventional methods, phenol and TCA, used for isolation of Gram-negative bacterial endotoxin. Their chemical composition, therefore, differs from that of Gram-negative bacterial endotoxin.

On the basis of tolerance studies it appears that similar non-specific host factors may be involved in the detoxification of both the streptococcal intracellular pyrogenic toxin and the Gram-negative bacterial endotoxin. Detoxification of streptococcal exotoxin requires a more immunologically specific mechanism.

Because all the Group A sonic extracts studied elicited reciprocal tolerance to one another, it is suggested that tolerance to the intracellular pyrogenic toxin is not correlated with type-specificity.