pacifarin

pa·cif·a·rin

(pə-sĭf′ər-ĭn)
n.
Any of various bacterial products that, introduced in small amounts, protect an organism from an infection or disease without killing the infectious agent.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.