Fig. 4

Photographs of the front (A) and side (B) view of the rectilinear scent evaluation apparatus. Cups containing culture sample solutions were placed within bars (C) that could be swung up and locked to position the sample beneath the holes along the floor of the apparatus. Rats were trained to walk from one side (beginning near the food pellet dispenser shown to the left in A) to the other, sniffing each sample in sequence as solenoids below the floor slid a metal plate to uncover each sample. Light emitting diodes (LEDS; pictured to the left of the floor holes along the white rail in B) illuminated when a hole was uncovered. Infrared emitting photobeams and sensors positioned within each hole registered when and for how long the rat inserted its nose. Flavored food pellets were automatically dispensed when the rat held its nose within a hole containing a Brucella-positive sample for the prescribed duration