 Image Number K5755-3 |
Rings shown on the plastic plate examined by ARS chemist Betty Burri reveal the amount of a vitamin-A-related protein in blood samples from volunteers.
Photo by Keith Weller
An official website of the United States government
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.