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Antigen.
An important consideration in the Wassermann reaction, as well as in other serum tests, is the nature of the antigen used. While, doubtless, individual workers obtain concordant results with various antigens, it has been the writer's experience that the human-heart extract, with cholesterin, as recommended by the Medical Research Committee, gives the most satisfactory and concordant results, if prepared in strict conformity with the instructions laid down by Fildes and McIntosh‡ and from fresh heart-muscle, the extract-heart-cholesterin being diluted 1 in 15 with normal physiological saline (0.85 per cent. NaCl).
[Footnote] ‡ P. Fildes and J. McIntosh, Brain, vol. 36, p. 193, 1913.
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This antigen, if accurately and carefully prepared, shows little inhibitory action upon the complement used: it is immaterial whether the heart is diseased or not; it should not, however, be decomposed, otherwise certain substances soluble in alcohol may be extracted which are in action inhibitory to complement.
One such antigen was prepared from a human heart removed at autopsy thirty-six hours after death and while not obviously decomposed. The resulting preparation deviated 0.75 minimum haemolytic doses (M.H.D.) of complement. The use of antigen prepared from guinea-pig heart was not found to be satisfactory, owing to a similar marked anti-complementary action.