Medical button help.

[artyfacts]

This button is made of copper, it is 1 inch wide or 25mm. It was completely in-cased in a mass of rock hard oxidization. I could not find this one listed in my books.

 

[72cheyenne]

It looks more like collar brass. I think WW1 or a little later.
http://www.hayesotoupalik.com/WW1 U.S. Uniforms.htm

 

[Mackaydon]

The 'caduceus' was formally adopted by the Medical Department of the United States Army in 1902. After World War I the caduceus was employed as an emblem by both the Army Medical Department and the Navy Hospital Corps.
Don....