In 1898, he discovered haemolytic sera and showed that the mechanism of their action on foreign blood is similar to that by which an antimicrobic serum acts on microbes and, furthermore, that the reactions of the sera are colloidal in nature.    From Wordnik.com.  [Jules Bordet - Biography] Reference

Bordet's early studies showed that antimicrobic sera include two active substances, one existing before immunization, known as alexine, and the other a specific antibody created by vaccination: he developed a method of diagnosing microbes by sera.    From Wordnik.com.  [Jules Bordet - Biography] Reference

The development of all antagonistic substances which confer the special character on antimicrobic sera, as well as antitoxins, may be expressed as the formation of bodies with specific combining affinity for the organic substance introduced into the system -- toxin, bacterium, red corpuscle, &c., as the case may be.    From Wordnik.com.  [Encyclopaedia Britannica, 11th Edition, Volume 3, Part 1, Slice 2 "Baconthorpe" to "Bankruptcy"] Reference