A negative stain colors the background of a smear rather than the bacteria as a direct stain does. These stains have negatively charged functional groups so they can’t bind directly to negatively charged bacteria. Kit Includes: 30mL Formalin-Nigrosin Solution 30mL Hydrochloric Acid, 1% 30mL Congo Red, 1% AQ DOT Info: Small quantity exemption 173.4 THIS PACKAGE CONFORMS TO 49 CFR 173.4 for domestic highway or rail transport only WARNING: This product can expose you to chemicals including Formaldehyde, Methanol and Benzidine-based dyes, which are known to the State of California to cause cancer and reproductive harm. For more information go to http://www.P65Warnings.ca.gov.