The pattern of development of symptoms was studied following injection of 3 MLD (minimum lethal dose) of tetanus toxin in each of the following sites in the rat: vein, muscle, endoneurium, epineurium, spinal cord, subarachnoid space, and subdural space. Similar observations were made when 3 MPD (minimum protective dose) of antitoxin were injected into each of the above sites a few minutes after the intramuscular injection of toxin.

Local tetanus followed intramuscular, endoneurial, and epineurial injection of the toxin; blood-borne tetanus also appeared in the latter instance. Tetanus dolorosus followed intraspinal injection of toxin. Both dorsal tetanus and blood-borne tetanus developed after subdural administration of toxin. Blood-borne tetanus, alone, appeared following intravenous and subarachnoid injection of toxin.

In no case did injection of antitoxin at the various sites listed above prevent local tetanus from developing after intramuscular injection of toxin. Of the various sites injected with antitoxin, the intramuscular, intraspinal, and intravenous were the most effective.

It is suggested that the endoneurial tissue spaces serve as a conduit for tetanus toxin from the muscle to the CNS. The perilemma of the peripheral nerve trunk may act as a selectively permeable membrane which permits tetanus toxin to pass from the epineurium to the endoneurium. Outward diffusion of toxin from the endoneurial spaces is apparently markedly reduced. The antitoxin probably is prevented from permeating this barrier in either direction. The importance of absorption of tetanus toxin by the lymphatic and blood circulation is discussed.

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