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The extensive employment of vaccines made from dead microorganisms has been followed by variable results; in some cases the results have been excellent, in others, absolutely negative. It seemed probable that these discrepancies might be due to the fact that in the one case an efficient quantity of the bacterial endotoxin had entered into the circulation, whereas when no beneficial results ensued it might be that a satisfactory extract of the microorganisms had not occurred. It therefore seemed logical to search for a means of dissolving the active principle of the bacteria with as little injury as possible.
After various methods had been unsuccessfully tried a solution was made by acting on the living microorganism with an alkaline pancreatin solution at 37 C. for a definite time, stopping the action by slight acidulation and filtering through a Pasteur filter. Studies with the pneumococcus showed that the virulence of the microorganism
HIRSCHFELDER JO. THE PRODUCTION OF ACTIVE AND PASSIVE IMMUNITY TO THE PNEUMOCOCCUS WITH A SOLUBLE VACCINEA PRELIMINARY REPORT. JAMA. 1912;LIX(15):1373–1374. doi:10.1001/jama.1912.04270100141011
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