Young adult mice were primed with 20 Lf (56 µg) of diphtheria toxoid and given a second injection of the same size 40 days later. This procedure produces a reproducible secondary response which can be used as a standard. Chloramphenicol in maximum dosage prevents the unknown process by which the animal is primed for the second response. To be fully inhibitory, the drug must be given from the hour of the first antigen injection in maximum dosage for 2 weeks. A delay of 48 hours in starting the drug allows completion of the priming process, and shorter delays produce partial inhibition. Hence the initiation of priming is a rapid process sensitive to chloramphenicol. Subsequent changes in the cell population necessary for the full development of priming are not sensitive to chloramphenicol.

The secondary antibody response is not inhibited in mice by chloramphenicol at the doses employed.

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