In Mary's personal letters....

[Eva Elisabeth]

Speaking of letters (can't find a better thread to add this question) - once more I just read that Mary had sustained severe physical damage while giving birth to Tad (plus the conclusion that it ended any intimate interaction). As the only source for this I've so far seen the sentence in one of her letters: "My disease is of a womanly nature". Is there any other source? If not, who was the first to name the "disease of womanly nature" "physical damage due to giving birth to Tad"?(The earliest I found was RP Rendell in "Mary Lincoln".) Also - I can't find a source for Tad being nicknamed Tad(pole) by his father
a) because his head reminded A. L. of a Tadpole (e.g. in Donald's "Lincoln", but without a reference) /
b) because he wiggled like a tadpole as an infant. This is on Wikipedia ( http://en.m.wikipedia.org/wiki/Tad_Lincoln ), and refers to a book I don't know: Wead, Doug (2003): "All The Presidents' Children".
Does anyone know??? (I guess my permanent asking for sources is somewhat annoying, sorry!)