Nearly all small serologic laboratories are confronted by the problem of securing guinea-pig serum for the Wassermann and other complement fixation tests. Where only a few tests are made at a time, and a pig is sacrificed each time for his blood, the expense often becomes greater than is justifiable. This may of course be partially overcome by bleeding the pig from the heart. Even so, considerable complement may be wasted, and another pig must be bled the next time tests are to be made.
Complement may be frozen and preserved at a low temperature (-15 C.) for several months, but most small laboratories are not equipped for such procedures.
Austin (The Journal, March 14, 1914, p. 868) advocated making a 40 per cent. dilution of the guinea-pig serum with 25 per cent. sodium chlorid solution. Then in his tests he used 0.6 per cent. salt solution instead of the