n :  a peroxidase that occurs in the horseradish (Armoracia lapathifolia of the mustard family), that produces a distinctive color when exposed to an appropriate solution, and that is used as a label for antibody-antigen complexes, as a cytochemical marker in immunohistochemical staining, and as a tracer to follow the course of individual neurons since it is transported by most neural pathways .
 
   
 
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