I thought it might have referred to a Piano Keyboard, but can't see what the 37D would refer to in this scenario. Then thought it might be something to do with the number of black keys on a standard piano, but there are only 36 !!
Om the other hand, 37D could mean 37 Degrees. 37 Degrees centigrade being the normal human body temperature.
But I'm sorry, this has got me baffled; would be pleased to see the answer