The change in surface tension behavior in the serum of sensitized guinea pigs is, as du Noüy has concluded for immunized rabbit serum, not referable to an antibody content, since we know that the capacity for transfer of sensitization remains in the serum indefinitely, while the increased time-drop phenomenon is a transitory manifestation. That this phenomenon cannot be invoked by a new antigen capable of calling out its specific antibody would seem to make this response one due to some basic stable alteration of a tissue active in the general process of sensitization: That this alteration is not one called out by such a simple toxic injury as a uranium nitrate nephritis is contributory evidence that the primary toxicity of the horse serum is not the specific factor involved.

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