In a preliminary report1 in The Journal a method was described by me for the preparation of a soluble vaccine against the pneumococcus, and the evidence presented of its efficacy in producing active and passive immunity. Ten cases of pneumonia treated with the extract were tabulated and reference was made to experiments with other micro-organisms. Since then, extracts have been prepared with greater accuracy by improved methods and the immunizing effects have been made more constant. At the same time, it has been found that these extracts are valuable as antigens in complement fixation for diagnostic purposes.
PREPARATION OF EXTRACTS
As the standardization of bacterial suspensions by the known methods of counting is notably uncertain, a gravimetric method was devised based on their opacity as compared by means of a delicate photometer with that of a suspension containing a known quantity of the microorganism as determined by its weight
HIRSCHFELDER JO. COMPLEMENT FIXATION IN DIAGNOSIS WITH BACTERIAL EXTRACTS PREPARED WITH DIGESTIVE FERMENTS. JAMA. 1915;LXV(24):2073–2076. doi:10.1001/jama.1915.02580240029008
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