These are both from pre-1975, I think. Each is a hardcover. Neither is
more than 8" tall or more than 1" thick, IIRC. One has a reddish-brown
cover, the other is blue; one has a linen covering; one has a female
author. Both are very detailed. I remember that one mentions the
possibility of a duel between Pasteur and an old doctor; one quotes a
man as saying jokingly to Pasteur, in effect: "what do you care about
France's beer industry - you don't even like beer;" one mentions a
formal party where Pasteur dons an informal frock-coat so his
underdressed friend (also wearing one) will not feel embarrassed; one
quotes a scientist as saying that it's easy to give anthrax to hens, so
Pasteur asks him to bring an infected hen; and both (I think) mention
the scene where it's argued that no one knows what the deadly puerpual
fever bacteria looks like, upon which Pasteur angrily limps to the
blackboard and draws it.

Any clues? Should I post this somewhere else?

Lenona.