Up to the present the most efficient method of studying iso-agglutinins in mice has been to suspend the erythrocytes in normal human serum, but experience has demonstrated this technic to be unreliable, particularly with the cells of C57BL mice. The enhancing power of a number of pathological sera was therefore tested; the sera from a number of cases of myelomatosis gave exceptionally good enhancement. This could be reduplicated by suspending the red cells in normal human serum and adding certain naturally occurring mucoid substances to the saline used as a vehicle for the dilution of antibody. Of these, pseudomucin from a human ovarian cyst was found to be most efficient.

Several preparations of dextran were tested, most of which gave intense rouleaux formation of mouse cells. One (“Intradex Salt Free”) gave excellent results and is now in routine use as a vehicle for antibody dilution.

We feel that the ability to obtain good agglutination of the cells of C57BL mice is an essential test of the efficiency of any system.

Technical failures have been found to be due to the following causes: (a) errors in the technic of reading, such as rough handling of the cells; (b) unsuitable preparations of dextran; and (c) inadequate immunization.

Certain antisera are inactive in the human serum-dextran system, particularly those produced in the A strain. It is probable that an antiglobulin test is essential in such cases.

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