Harnack's Theorem in real algebraic geometry states the following: If $X$ is a nonsingular projective curve of genus $g$ defined over $\mathbb{R}$ then the number of connected components of $X(\mathbb{R})$ is $\leq g+1$.
Harnack proved this using Bezout's theorem. I would like a reference to Harnack's proof of Harnack's theorem. (I am not interested in Klein's proof or any of the other proofs of this theorem.)
Harnack's inequality is proved with Harnack's original proof in the book "Real algebraic geometry" by Bochnak, Coste and Roy.