The electrophoretic fractions of serum proteins were studied up to the 5th generation in a colony of germ-free rats. The germ-free animals had significantly lower concentrations of beta and the gamma globulins, while the other fractions were within normal limits.

Assuming that the gamma globulins survive equally long in the circulation in germ-free animals as in controls, the production of gamma globulins in normal rats is three times as rapid as in germ-free rats. This suggests that the normal flora of microorganisms is an important stimulant for the gamma globulin-producing cells.

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