Humoral antibodies and a certain degree of resistance to infection with vaccinia, probably not enduring, are produced in rabbits by the repeated injections of inactive formolized (0.3 per cent) elementary bodies of vaccinia and virus-free filtrates of dermal vaccine virus. Single injections of large amounts of elementary bodies are not as effective as similar amounts administered in small repeated doses. Drastic treatment (10 per cent formaldehyde or boiling for 2 hours) almost completely alters or destroys the antigenicity of elementary bodies.

It appears that the production of precipitins and agglutinins does not parallel that of neutralizing antibodies and that the mere presence of such antibodies in the serum of a rabbit as the result of injections of inactive elementary bodies does not necessarily indicate that the animal possesses a great degree of resistance to infection with a potent vaccine virus.

The fact that some neutralizing antibodies appeared in the sera of rabbits that had received injections of inactive elementary bodies can be interpreted as indicating that at least not all neutralizing antibodies for vaccine virus are the result of a reaction to an antigen produced by the host in consequence of a vaccinal infection.

No evidence was obtained to show that elementary bodies inactivated by our methods (0.3 per cent formaldehyde) would serve as a suitable vaccine for the protection of human beings against smallpox.

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