Sulfanilamide prevents the evolution of an invariably fatal streptococcus empyema in rabbits when it is given repeatedly and in sufficient doses subcutaneously. Complete sterilization of the inoculated cavity occurs on approximately the 2nd day. The serum, defibrinated blood and artificial pleural exudate of similarly treated animals inhibits the growth of the same streptococcus in the test tube but even repeated doses of such treated blood serum fail to sterilize the culture. The coccal chains grown in such drugged serum are elongated and present pleomorphic and metachromatic organisms and may give rise to colonies that are at first less predominantly mucoid in appearance. Such organisms have, however, lost little if any of their virulence.

Cooperation on the part of locally derived clasmatocytes is apparently required in complete sterilization of the animal body. This conclusion is reached not only by a process of exclusion from comparison with the test tube results, but through the direct histological demonstration of a precocious and increasing mobilization of clasmatocytes in the parietal and visceral pleura of treated animals.

In other words, sulfanilamide apparently produces a bacteriostasis sufficiently marked to protect the accumulated leucocytes and to allow the natural defense macrophages to accumulate. There is direct evidence that the drug does not in itself stimulate the mobilization of the macrophages. There is no evidence that the cell reaction which finally accounts for disposal of the organisms is other than local.

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