It is conceded by most observers that in working with a hemolytic system it is advisable to use known amounts of both amboceptor and cells. Wassermann's original method for the diagnosis of syphilis makes use of 1 c.c. of a 5 per cent. suspension of sheep corpuscles with just twice the amount of amboceptor necessary to hemolyze these cells. Since the discovery of the existence of an antisheep amboceptor in some human serums it has been a question whether this additional amount of amboceptor might not be sufficient to produce hemolysis in conjunction with a small residue of complement not fixed in the first stage of the reaction. If this should occur negative results would thus be obtained in syphilitic cases.
The recognition of this possibility has given rise to several modifications of the Wassermann reaction. The best-known of these is probably that of Noguchi. He maintained1