Abstract
Patients who are being given fever therapy by means of intravenous injections of typhoid vaccine exhibit a decreasing reactivity, and must be given larger and larger doses of the vaccine in order to develop similar fevers at successive treatments. After several injections some individuals may require doses as large as 250 ml of typhoid vaccine in a single day. 1 The mechanism of this remarkable tolerance has not been explained. The present report deals with a study of the phenomenon in rabbits.
The rabbits used were males, of mixed breed, weighing 2 to 3 kg. During test periods they were placed in wooden stalls, and held by head boards. Rectal temperatures were taken at 30-minute intervals, through openings in the floors of the stalls. Observations were never continued for more than 7 hours after giving vaccine, to prevent undue fatigue of the animals. The vaccine used contained approximately one billion killed E. typhosa per ml.† The dose was 1 ml of a 1:8 dilution in physiologic salt solution. The agent used for blockade of the reticulo-endothelial system was colloidal thorium dioxide (Thorotrast-Heyden Co.); 9 ml was injected intravenously.
The febrile responses to daily injections of the same dose of vaccine were recorded on 40 rabbits during periods of from 8 to 45 days. The first injection of vaccine always caused a rise in body temperature of 4-5°F, and some fever persisted throughout the 7-hour period of observation. The 2nd and 3rd injections generally caused almost as much fever as the first, but after that there was a decrease in reaction until the 6th to 10th day. Additional injections caused no further diminution, each one inducing approximately
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