Kits including novel fluorescent derivitization reagents for labeling an aldehyde- andor ketone-containing target substance in a sample are described. An apparatus for modulating an intensity of a radiation beam generated by a radiation source includes a filter, and a positioner secured to the filter, the positioner configured to move the filter relative to the radiation source. The trunk loop includes a back strap which in use of the harness lies across the back of the animal affixed to a lower strap which in use of the harness passes under the animal behind the forelegs. The combining logic combines a current picture with a prediction picture to produce a combined picture.