bracken: large coarse fern often several feet high; essentially weed ferns; cosmopolitan
fern: any of numerous flowerless and seedless vascular plants having true roots from a rhizome and fronds that uncurl upward; reproduce by spores
complement fixation test: a blood test in which a sample of serum is exposed to a particular antigen and complement in order to determine whether or not antibodies to that particular antigen are present; used as a diagnostic test