When did the phrase "glass stomach" originate and what's its meaning?

From what I've found, there are actually two things to which the term "glass stomach" can apply.

The first term is more correctly known as "hourglass stomach" - a deformity in which the stomach is constricted into an hourglass shape. This may be a congenital defect or it may be caused by something else, like ulcers. According to one article I've read, the earliest operative treatment occurred in 1889.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1426633/?page=1

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1425038/?page=1

The second use of the term "glass stomach" refers to a clear portal, known as a fistula, that can be installed in cows, to allow for easier study of their digestive process.

http://www.jgi.doe.gov/News/news_11_01_27.html