Of papers recently published which concern the properties of immune-sera and bear upon the general theory of immunity one of the most important is that of Bordet2 on antisensibilisatrices (anti-immunebodies, anti-amboceptors). This observer obtained an anti-immune-body by injecting the serum of a normal animal (rabbit) into an animal of another species (guinea-pig), and found that there was developed an anti-immune-body which had the property of neutralising the various immune-bodies which might be developed by active immunisation of the first animal. In this way a certain community as regards combining properties was demonstrated among the immune-bodies of a given species of animal. He studied the properties of the anti-immune-body, and in particular showed that it did not combine with the cytophile group of the immune-body, and therefore did not prevent the usual combination of the cell-receptor with the immune-body. This fact he held to be inconsistent with Ehrlich's views regarding the amboceptor constitution of immune-body. His observations on the neutralising effect of the anti-immune-body were carried out by means of haemolytic sera. Ehrlich and Sachs3 confirmed the chief results obtained by Bordet, but so far from admitting the establishment of any objection to the amboceptor theory, claimed that they supplied strong evidence in support of it. They maintained in fact that the anti-immune-body acted by combining with the com piementophile group of the amboceptor, and thus prevented the union of complement, stating also that the results showed that the various immune-bodies from the same species had a similar complementophile apparatus. The theoretical bearings of the facts established will, however, be discussed later.