To the Editor:
—Regarding the communication of Dr. Hindman (The Journal, May 25, 1918, p. 1561) in which he states that "sodium acetate [recommended by me for preservation of complement, The Journal, Sept. 22, 1917] forms a precipitate with some guinea-pig serums," let me state, after considerable experience with this method, that no such precipitate occurs from acetate solutions up to 25 per cent. strength. Solutions above this strength may cause a crystalline precipitate, which can be sedimented off and does not interfere in any way with the complement fixation reaction.In regard to his observation as to the possibility of getting a negative reaction in a weakly positive case, on account of the sharp reaction or possible overaction of acetated complement, allow me to suggest that this is a matter entirely of exact technic.In my experience, which has been entirely with guinea-pig serum, I found that in using