In the course of certain experiments it became important for us to inform ourselves as accurately as possible as to the absolute or relative specificity of opsonins, the close resemblance in nature between opsonins, precipitins, agglutinins, etc., preparing us for the statement that they are specific.
This is not, however, as yet entirely proved. Wright and Douglas and Bullock1 seem satisfied about it, and Bullock made experiments as follows: Serum was digested with staphylococci at 37° C. (98.6° F.) and then freed of the organisms by centrifugalization, after which it was found to have lost all opsonic power for staphylococci, though it largely retained that for tubercle bacilli. Conversely, when digested at 37° C. (98.6° F.) with tubercle bacilli and then centrifugalized, it had lost the opsonin for the tubercle bacillus, though it retained it for the staphylococcus.
Potter, Ditman and Bradley,2 however, came to different experimental results
McFARLAND J, L'ENGLE EM. THE SPECIFIC NATURE OF OPSONINS.. JAMA. 1907;XLIX(14):1178–1181. doi:10.1001/jama.1907.25320140024001g